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/api/tooling/spec.json

@@ -1947,6 +1947,15 @@
             "description": "Filter by label matchers encoded as JSON representations of Prometheus matchers (for example, {\"type\":0,\"name\":\"severity\",\"value\":\"critical\"}). Provide one matcher per query string value.",
             "name": "matcher",
             "in": "query"
+          },
+          {
+            "type": "array",
+            "items": {
+              "type": "string"
+            },
+            "description": "Filter rules by their static labels (not alert instance labels). Each value is a JSON-encoded Prometheus-like matcher (for example, {\"type\":0,\"name\":\"severity\",\"value\":\"critical\"}).\nFor equality matchers with empty string values (e.g., name=\"\"), rules that have the label with an empty value OR rules without the label will match (standard Prometheus behavior).",
+            "name": "rule_matcher",
+            "in": "query"
           }
         ],
         "responses": {