unified-storage: Reduce calls to the user service (#102934)

* Create ListByIdOrUID in user service

* create UnstructuredToLegacyFolderList 

* update GetFolders to use list parser

* update GetDescendants to use list parser

* update UnstructuredToLegacyFolder to also make a single call to the user service

---------

Co-authored-by: Stephanie Hingtgen <stephanie.hingtgen@grafana.com>

pkg/services/user/userimpl/user_test.go

@@ -274,6 +274,7 @@ type FakeUserStore struct {
 	ExpectedError                           error
 	ExpectedDeleteUserError                 error
 	ExpectedCountUserAccountsWithEmptyRoles int64
+	ExpectedListUsersByIdOrUid              []*user.User
 }
 
 func newUserStoreFake() *FakeUserStore {
@@ -296,6 +297,10 @@ func (f *FakeUserStore) GetByUID(context.Context, string) (*user.User, error) {
 	return f.ExpectedUser, f.ExpectedError
 }
 
+func (f *FakeUserStore) ListByIdOrUID(context.Context, []string, []int64) ([]*user.User, error) {
+	return f.ExpectedListUsersByIdOrUid, f.ExpectedError
+}
+
 func (f *FakeUserStore) LoginConflict(context.Context, string, string) error {
 	return f.ExpectedError
 }