Implement custom Json Marshaller for AssessmentReport struct

[sanyamsinghal]

Describe the changes in this pull request

• using this we can achieve different content in json output for assessment report vs ybd payload

Assessment Report struct

type AssessmentReport struct {
	VoyagerVersion                 string                                `json:"VoyagerVersion"`
	TargetDBVersion                *ybversion.YBVersion                  `json:"TargetDBVersion"`
	MigrationComplexity            string                                `json:"MigrationComplexity"`
	MigrationComplexityExplanation string                                `json:"MigrationComplexityExplanation"`
	SchemaSummary                  utils.SchemaSummary                   `json:"SchemaSummary"`
	Sizing                         *migassessment.SizingAssessmentReport `json:"Sizing"`
	Issues                         []AssessmentIssue                     `json:"-"` // disabled in reports till corresponding UI changes are done(json and html reports)
	TableIndexStats                *[]migassessment.TableIndexStats      `json:"TableIndexStats"`
	Notes                          []string                              `json:"Notes"`
	SerializationMode              string                                `json:"-"` // field to control serialization of json

	// fields going to be deprecated
	UnsupportedDataTypes       []utils.TableColumnsDataTypes     `json:"UnsupportedDataTypes"`
	UnsupportedDataTypesDesc   string                            `json:"UnsupportedDataTypesDesc"`
	UnsupportedFeatures        []UnsupportedFeature              `json:"UnsupportedFeatures"`
	UnsupportedFeaturesDesc    string                            `json:"UnsupportedFeaturesDesc"`
	UnsupportedQueryConstructs []utils.UnsupportedQueryConstruct `json:"UnsupportedQueryConstructs"`
	UnsupportedPlPgSqlObjects  []UnsupportedFeature              `json:"UnsupportedPlPgSqlObjects"`
	MigrationCaveats           []UnsupportedFeature              `json:"MigrationCaveats"`
}

For ybd we need all the fields.
For Assessment report json we only need the fields before the comment - // fields going to be deprecated

Have to add a extra field SerializationMode just for the purpose of marshalling, this won't be transmitted further(only in memory).

Describe if there are any user-facing changes

NA

How was this pull request tested?

Existing test enough.

Does your PR have changes that can cause upgrade issues?

Component	Breaking changes?
MetaDB	No
Name registry json	No
Data File Descriptor Json	No
Export Snapshot Status Json	No
Import Data State	No
Export Status Json	No
Data .sql files of tables	No
Export and import data queue	No
Schema Dump	No
AssessmentDB	No
Sizing DB	No
Migration Assessment Report Json	No (not json actually, but struct has changed which shouldn't impact upgradability)
Callhome Json	No
YugabyteD Tables	No
TargetDB Metadata Tables	No

[sanyamsinghal]

closing this, as already covered in - #2237