NGAlert: Migrate old notification channel config (#33846)

* NGAlert: Migrate old notification channel config

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Copy the required structs and functions

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Fix lint

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Fix review comments and error on discontinued channels

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Use both ID and UID to map channels, attach UID to channels

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Fix lint

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Bug fixes

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Use alert table instead of dashboard for channel IDs

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Fix offline reviews: don't add empty receivers and routes, add receiver for unmigrated channels

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Handle multiple default channels, pick default from used channels

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

* Include default channels in all receivers

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

pkg/services/sqlstore/migrations/ualert/dash_alert.go

@@ -21,8 +21,8 @@ type dashAlert struct {
 }
 
 var slurpDashSQL = `
-SELECT id, 
-	org_id, 
+SELECT id,
+	org_id,
 	dashboard_id,
 	panel_id,
 	org_id,
@@ -70,7 +70,8 @@ type dashAlertSettings struct {
 // dashAlertNot is the object that represents the Notifications array in
 // dashAlertSettings
 type dashAlertNot struct {
-	UID string `json:"uid"`
+	UID string `json:"uid,omitempty"`
+	ID  int64  `json:"id,omitempty"`
 }
 
 // dashAlertingConditionJSON is like classic.ClassicConditionJSON except that it