[release-12.1.2] Alerting: Add keepFiringFor and missing_series_evals_to_resolve to file provisioning (#109710)

* Alerting: Add keepFiringFor and missing_series_evals_to_resolve to file provisioning (#109699)

* Fix MissingSeriesEvalsToResolve type

pkg/tests/api/alerting/test-data/provisioning-rules.yaml

@@ -62,6 +62,10 @@ groups:
         execErrState: Alerting
         # <duration, required> for how long should the alert fire before alerting
         for: 60s
+        # <duration> for how long the alert should keep firing after condition stops being true
+        keepFiringFor: 120s
+        # <int> number of evaluation intervals required to resolve alert when data is missing
+        missing_series_evals_to_resolve: 3
         # <map<string, string>> a map of strings to pass around any data
         annotations:
           some_key: some_value