Alerting: Allow hooking into request handler functions. (#67000)

* Alerting: Allow hooking into request handler functions.

Adds a facility to AlertNG for hooking into API handlers, allowing the
replacement of request handlers for specific paths. One of goals of this
approach was to allow hooking as late as possible in the request, e.g.
after all middleware has been applied, to simplfiy usage.

* Update pkg/services/ngalert/api/hooks.go

Co-authored-by: gotjosh <josue.abreu@gmail.com>

* Update pkg/services/ngalert/api/hooks.go

Co-authored-by: gotjosh <josue.abreu@gmail.com>

* Update pkg/services/ngalert/ngalert.go

Co-authored-by: gotjosh <josue.abreu@gmail.com>

* Fixes to review comments

* Fix passing logger in

---------

Co-authored-by: gotjosh <josue.abreu@gmail.com>

pkg/services/ngalert/api/generated_base_api_testing.go

@@ -68,7 +68,7 @@ func (api *API) RegisterTestingApiEndpoints(srv TestingApi, m *metrics.API) {
 			metrics.Instrument(
 				http.MethodPost,
 				"/api/v1/rule/backtest",
-				srv.BacktestConfig,
+				api.Hooks.Wrap(srv.BacktestConfig),
 				m,
 			),
 		)
@@ -78,7 +78,7 @@ func (api *API) RegisterTestingApiEndpoints(srv TestingApi, m *metrics.API) {
 			metrics.Instrument(
 				http.MethodPost,
 				"/api/v1/eval",
-				srv.RouteEvalQueries,
+				api.Hooks.Wrap(srv.RouteEvalQueries),
 				m,
 			),
 		)
@@ -88,7 +88,7 @@ func (api *API) RegisterTestingApiEndpoints(srv TestingApi, m *metrics.API) {
 			metrics.Instrument(
 				http.MethodPost,
 				"/api/v1/rule/test/{DatasourceUID}",
-				srv.RouteTestRuleConfig,
+				api.Hooks.Wrap(srv.RouteTestRuleConfig),
 				m,
 			),
 		)
@@ -98,7 +98,7 @@ func (api *API) RegisterTestingApiEndpoints(srv TestingApi, m *metrics.API) {
 			metrics.Instrument(
 				http.MethodPost,
 				"/api/v1/rule/test/grafana",
-				srv.RouteTestRuleGrafanaConfig,
+				api.Hooks.Wrap(srv.RouteTestRuleGrafanaConfig),
 				m,
 			),
 		)