Alerting: Add rule_matcher filter to Prometheus rules API (#115297)

**What is this feature?**

Add `rule_matcher` filter to the Prometheus-compatible list rules API: `/api/prometheus/grafana/api/v1/rules`. It allows to filter rules by static labels (not by alert instance labels).

**Special notes:**
  - Equality (`=`) and inequality (`!=`) matchers are pushed down to the database. Regex matchers (`=~`, `!~`) are applied in-memory at the API layer.
  - SQLite: Uses GLOB pattern matching
  - MySQL / PostgreSQL: Use JSON functions to compare label values


---------

Co-authored-by: Konrad Lalik <konradlalik@gmail.com>

pkg/services/ngalert/models/alert_rule.go

@@ -18,6 +18,7 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"github.com/google/go-cmp/cmp/cmpopts"
 
+	"github.com/prometheus/alertmanager/pkg/labels"
 	prommodels "github.com/prometheus/common/model"
 
 	"github.com/grafana/grafana-plugin-sdk-go/data"
@@ -1012,6 +1013,10 @@ type ListAlertRulesQuery struct {
 	SearchRuleGroup string
 
 	HasPrometheusRuleDefinition *bool
+
+	// LabelMatchers filters rules by their labels.
+	// Only equality and inequality matchers are supported, no regex operators.
+	LabelMatchers labels.Matchers
 }
 
 type ListAlertRulesExtendedQuery struct {