Adding Permissions to User Struct

[jeevanragula]

Description

Get Account API doesn't return Permission details. So I am adding Permissions in the User struct.
This will fix #673

Testing plan

External links

Output from tests

Including output from tests may require access to a TFE instance. Ignore this section if you have no environment to test against.

$ TFE_ADDRESS="https://example" TFE_TOKEN="example" go test ./... -v -run TestFunctionsAffectedByChange

?       github.com/hashicorp/go-tfe/examples/configuration_versions     [no test files]
?       github.com/hashicorp/go-tfe/examples/organizations      [no test files]
?       github.com/hashicorp/go-tfe/examples/registry_modules   [no test files]
?       github.com/hashicorp/go-tfe/examples/users      [no test files]
?       github.com/hashicorp/go-tfe/examples/workspaces [no test files]
?       github.com/hashicorp/go-tfe/mocks       [no test files]
=== RUN   TestUsersReadCurrent
=== RUN   TestUsersReadCurrent/two_factor_options_are_decoded
=== RUN   TestUsersReadCurrent/permissions_are_decoded
--- PASS: TestUsersReadCurrent (1.67s)
    --- PASS: TestUsersReadCurrent/two_factor_options_are_decoded (0.00s)
    --- PASS: TestUsersReadCurrent/permissions_are_decoded (0.00s)
PASS
ok      github.com/hashicorp/go-tfe     1.854s


...

[hashicorp-cla]

All committers have signed the CLA.

[jeevanragula]

@barrettclark @nfagerlund @brandonc I could see you are in the approver list for this repository.
Can you please check this PR and issue?

[brandonc]

Thank you for the thorough contribution! My feedback is minor and I'll be happy to merge it once it's addressed

[jeevanragula]

@brandonc Thanks for the suggestions. Updated the PR now.

[github-actions]

Reminder to the contributor that merged this PR: if your changes have added important functionality or fixed a relevant bug, open a follow-up PR to update CHANGELOG.md with a note on your changes.