Object store: get user from context (#56346)

* GRPC Server: Add signedInUser to context after auth

* add permissions to signedInUser

* add access control permissions test

* add additional signedInUser checks

* get user from context

* move `UserFromContext` to object/auth.go

Co-authored-by: Todd Treece <todd.treece@grafana.com>

pkg/services/store/object/tests/server_integration_test.go

@@ -149,8 +149,8 @@ func TestObjectServer(t *testing.T) {
 	ctx = metadata.AppendToOutgoingContext(ctx, "authorization", fmt.Sprintf("Bearer %s", testCtx.authToken))
 
 	fakeUser := &object.UserInfo{
-		Login: "fake",
-		Id:    1,
+		Login: testCtx.user.Login,
+		Id:    testCtx.user.UserID,
 	}
 	firstVersion := "1"
 	kind := "dashboard"