Alerting: update rules POST API to validate query and condition only for rules that changed. (#68667)

* replace condition validation with just structural validation
* validate conditions of only new and updated rules
* add integration tests for rule update\delete API

Co-authored-by: George Robinson <george.robinson@grafana.com>

pkg/services/ngalert/api/api_testing.go

@@ -55,9 +55,6 @@ func (srv TestingApiSrv) RouteTestGrafanaRuleConfig(c *contextmodel.ReqContext,
 			UID:   body.NamespaceUID,
 			Title: body.NamespaceTitle,
 		},
-		func(condition ngmodels.Condition) error {
-			return srv.evaluator.Validate(eval.NewContext(c.Req.Context(), c.SignedInUser), condition)
-		},
 		srv.cfg,
 	)
 	if err != nil {