Alerting: Migrate to integration schema (#111643)

* update tests to assert against snapshot
* remove channel_config package replaced by schemas from alerting module
* update  references to use new schema

pkg/tests/api/alerting/test-data/alert-notifiers-v2-snapshot.json

@@ -7,6 +7,7 @@
     "description": "Send notifications to LINE notify",
     "versions": [
       {
+        "typeAlias": "line",
         "version": "v1",
         "canCreate": true,
         "options": [
@@ -8143,7 +8144,7 @@
     "type": "sns",
     "currentVersion": "v1",
     "name": "AWS SNS",
-    "heading": "Webex settings",
+    "heading": "AWS SNS settings",
     "description": "Sends notifications to AWS Simple Notification Service",
     "versions": [
       {