Alerting: Notifications Routes API (#91550)

* Introduce new models RoutingTree, RouteDefaults and Route and api-server to serve them that is backed by provisioning notification policy service.

* update method UpdatePolicyTree of notification policy service to return route and new version

* declare new actions alert.notifications.routes:read and alert.notifications.routes:write and two corresponding fixed roles.

---------

Co-authored-by: Tom Ratcliffe <tom.ratcliffe@grafana.com>
Co-authored-by: Matthew Jacobson <matthew.jacobson@grafana.com>

apps/alerting/notifications/Makefile

@@ -0,0 +1,4 @@
+.PHONY: generate
+generate:
+	## --crdencoding none is needed to avoid infinite loop while generating recursive models'
+	grafana-app-sdk generate -c . -g ./apis --crdencoding none

apps/alerting/notifications/routingtree.cue

@@ -0,0 +1,49 @@
+package core
+
+route: {
+	kind:  "RoutingTree"
+	group: "notifications"
+	apiResource: {
+		groupOverride: "notifications.alerting.grafana.app"
+	}
+	codegen: {
+		frontend: false
+		backend:  true
+	}
+	pluralName: "RoutingTrees"
+	current:    "v0alpha1"
+	versions: {
+		"v0alpha1": {
+			schema: {
+				#RouteDefaults: {
+					receiver: string
+					group_by?: [...string]
+					group_wait?: string
+					group_interval?:  string
+					repeat_interval?: string
+				}
+				#Matcher: {
+					 type: "=" |"!="|"=~"|"!~" @cuetsy(kind="enum")
+					 label: string
+					 value: string
+				}
+				#Route: {
+					receiver?: string
+					matchers?: [...#Matcher]
+					continue: bool
+
+					group_by?: [...string]
+					mute_time_intervals?: [...string]
+					routes?: [...#Route]
+					group_wait?: string
+					group_interval?:  string
+					repeat_interval?: string
+				}
+				spec: {
+					 defaults: #RouteDefaults
+					 routes: [...#Route]
+				}
+			}
+		}
+	}
+}