Alerting: Send information about alert rule to data source in headers (#90344)

* add support of metadata to condition and adding it to request headers
* support for additional metadata when condition is built
* add additionall context to conditions: source and folder title
* add version
* use percent-encoding for header values

pkg/services/ngalert/api/api_testing.go

@@ -83,7 +83,7 @@ func (srv TestingApiSrv) RouteTestGrafanaRuleConfig(c *contextmodel.ReqContext,
 		}
 	}
 
-	evaluator, err := srv.evaluator.Create(eval.NewContext(c.Req.Context(), c.SignedInUser), rule.GetEvalCondition())
+	evaluator, err := srv.evaluator.Create(eval.NewContext(c.Req.Context(), c.SignedInUser), rule.GetEvalCondition().WithSource("preview"))
 	if err != nil {
 		return ErrResp(http.StatusBadRequest, err, "Failed to build evaluator for queries and expressions")
 	}