Alerting: Add OAuth2 Support for Webhook Receiver (#106302)

* Add to available channels

* Export

* Fix bug in deeply nested secrets

BE: Slice re-use bug when traversing deeply.

FE: Only at most one level of nesting was being taken into account
when determining secureFields keys. This change adds a new field on
NotificationChannelOption: secureFieldKey. This is populated on API GET via
transform. This change gives us the option to hardcode secureFieldKey in the
backend and no longer calculate the key via settings topology.

* Update grafana/alerting to 3e20fda3b872

* Prettier

* Linting

* Fix IntegrationConfig test to catch secure field mismatch

go.mod

@@ -77,7 +77,7 @@ require (
 	github.com/googleapis/gax-go/v2 v2.14.1 // @grafana/grafana-backend-group
 	github.com/gorilla/mux v1.8.1 // @grafana/grafana-backend-group
 	github.com/gorilla/websocket v1.5.4-0.20250319132907-e064f32e3674 // @grafana/grafana-app-platform-squad
-	github.com/grafana/alerting v0.0.0-20250605155607-02235095d018 // @grafana/alerting-backend
+	github.com/grafana/alerting v0.0.0-20250610043455-3e20fda3b872 // @grafana/alerting-backend
 	github.com/grafana/authlib v0.0.0-20250515162837-2f4a8263eabb // @grafana/identity-access-team
 	github.com/grafana/authlib/types v0.0.0-20250325095148-d6da9c164a7d // @grafana/identity-access-team
 	github.com/grafana/dataplane/examples v0.0.1 // @grafana/observability-metrics