chore: Use Mockery instead of manually created mocks for encryption_at_rest unit tests

[oarbusi]

Description

Use Mockery instead of manually created mocks for encryption_at_rest unit tests

Link to any related issue(s): https://jira.mongodb.org/browse/CLOUDP-214983

Type of change:

• Bug fix (non-breaking change which fixes an issue). Please, add the "bug" label to the PR.
• New feature (non-breaking change which adds functionality). Please, add the "enhancement" label to the PR.
• Breaking change (fix or feature that would cause existing functionality to not work as expected). Please, add the "breaking change" label to the PR.
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the contribution guidelines
• I have checked that this change does not generate any credentials and that they are NOT accidentally logged anywhere.
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirements
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code
• If changes include deprecations or removals, I defined an isolated PR with a relevant title as it will be used in the auto-generated changelog.

Further comments

[github-actions]

Package	Line Rate	Health
github.com/mongodb/terraform-provider-mongodbatlas/internal/common/conversion	31%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/common/dsschema	100%	✔
github.com/mongodb/terraform-provider-mongodbatlas/internal/common/validate	68%	➖
github.com/mongodb/terraform-provider-mongodbatlas/internal/provider	7%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/accesslistapikey	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/advancedcluster	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/alertconfiguration	33%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/apikey	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/atlasuser	0%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/auditing	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/backupcompliancepolicy	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/cloudbackupschedule	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/cloudbackupsnapshot	5%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/cloudbackupsnapshotexportbucket	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/cloudbackupsnapshotexportjob	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/cloudbackupsnapshotrestorejob	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/cloudprovideraccess	4%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/cluster	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/clusteroutagesimulation	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/customdbrole	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/customdnsconfigurationclusteraws	5%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/databaseuser	30%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/datalakepipeline	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/encryptionatrest	31%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/eventtrigger	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/federateddatabaseinstance	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/federatedquerylimit	4%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/federatedsettingsidentityprovider	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/federatedsettingsorgconfig	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/federatedsettingsorgrolemapping	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/globalclusterconfig	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/ldapconfiguration	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/ldapverify	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/maintenancewindow	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/networkcontainer	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/networkpeering	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/onlinearchive	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/organization	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/orginvitation	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/privateendpointregionalmode	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/privatelinkendpoint	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/privatelinkendpointserverless	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/privatelinkendpointservice	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/privatelinkendpointservicedatafederationonlinearchive	3%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/privatelinkendpointserviceserverless	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/project	30%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/projectapikey	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/projectinvitation	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/projectipaccesslist	10%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/rolesorgid	7%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/searchdeployment	23%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/searchindex	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/serverlessinstance	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/streamconnection	26%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/streaminstance	14%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/teams	1%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/thirdpartyintegration	4%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/service/x509authenticationdatabaseuser	2%	❌
github.com/mongodb/terraform-provider-mongodbatlas/internal/testutil/acc	4%	❌
Summary	7% (765 / 11018)	❌

[andreaangiolillo]

LGTM