Annotations: Optimize search by tags (#93547)

* Annotations: Optimize search on large number of dashboards

* refactor

* fix batch size

* Return early if no annotations found

* revert go.mod

* return nil in case of error

* Move default limit to the API package

* fix empty access control filter

* Set default limit to 100

* optimize query when number of annotations is less than limit

* Update pkg/services/annotations/annotationsimpl/annotations.go

Co-authored-by: Ieva <ieva.vasiljeva@grafana.com>

* remove limit from store since it's set in API

* set default limit in Find method (do not break tests)

* Only add limit to the query if it's set

* use limit trick for all searches without dashboard filter

* set default page if not provided

---------

Co-authored-by: Ieva <ieva.vasiljeva@grafana.com>

pkg/api/annotations.go

@@ -22,6 +22,8 @@ import (
 	"github.com/grafana/grafana/pkg/web"
 )
 
+const defaultAnnotationsLimit = 100
+
 // swagger:route GET /annotations annotations getAnnotations
 //
 // Find Annotations.
@@ -48,6 +50,9 @@ func (hs *HTTPServer) GetAnnotations(c *contextmodel.ReqContext) response.Respon
 		MatchAny:     c.QueryBool("matchAny"),
 		SignedInUser: c.SignedInUser,
 	}
+	if query.Limit == 0 {
+		query.Limit = defaultAnnotationsLimit
+	}
 
 	// When dashboard UID present in the request, we ignore dashboard ID
 	if query.DashboardUID != "" {