Audit logging - new schema (#20447)

* Audit logging - new schema added, old schema removed.

* fix linter error by running goimports

* Address review comments

* Address review comments

* Example usage of new audit logging API for the updateUserAuth call

* fixed unit test on auditing updating user record

* Changed the `TestUpdateConfigDiffInAuditRecord` testcase---it failed, because this PR changes how the `meta` field is serialized into the audit log records.

* fix linter error

model/user.go

@@ -140,6 +140,12 @@ type UserAuth struct {
 	AuthService string  `json:"auth_service,omitempty"`
 }
 
+func (u *UserAuth) Auditable() map[string]interface{} {
+	return map[string]interface{}{
+		"auth_service": u.AuthService,
+	}
+}
+
 //msgp:ignore UserForIndexing
 type UserForIndexing struct {
 	Id          string   `json:"id"`
@@ -829,6 +835,13 @@ func (u *User) ToPatch() *UserPatch {
 	}
 }
 
+func (u *User) Auditable() map[string]interface{} {
+	return map[string]interface{}{
+		"id":       u.Id,
+		"username": u.Username,
+	}
+}
+
 func (u *UserPatch) SetField(fieldName string, fieldValue string) {
 	switch fieldName {
 	case "FirstName":