MM-53924 - Implement push notifications plugin hook and plugin api method (#24350)

* Revert "MM-52804 - Implement SendPushNotification plugin api method (#24273)"

This reverts commit 8418eefb75.

* Revert "MM-53924 - Implement NotificationWillBePushed plugin hook (#24263)"

This reverts commit f13a531bca.

* implement NotificationWillBePushed plugin hook

* implement SendPushNotification plugin api method

* move where we're setting post and channel type

* fix comment

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/notification_push_test.go

@@ -1468,6 +1468,7 @@ func TestPushNotificationRace(t *testing.T) {
 	require.NoError(t, err)
 	s.products["channels"] = ch
 
+	app := New(ServerConnector(s.Channels()))
 	require.NotPanics(t, func() {
 		s.createPushNotificationsHub(th.Context)
 
@@ -1475,9 +1476,9 @@ func TestPushNotificationRace(t *testing.T) {
 
 		// Now we start sending messages after the PN hub is shut down.
 		// We test all 3 notification types.
-		th.App.clearPushNotification("currentSessionId", "userId", "channelId", "")
+		app.clearPushNotification("currentSessionId", "userId", "channelId", "")
 
-		th.App.UpdateMobileAppBadge("userId")
+		app.UpdateMobileAppBadge("userId")
 
 		notification := &PostNotification{
 			Post:    &model.Post{},
@@ -1487,7 +1488,7 @@ func TestPushNotificationRace(t *testing.T) {
 			},
 			Sender: &model.User{},
 		}
-		th.App.sendPushNotification(notification, &model.User{}, true, false, model.CommentsNotifyAny)
+		app.sendPushNotification(notification, &model.User{}, true, false, model.CommentsNotifyAny)
 	})
 }