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/public/plugin/hooks.go

@@ -287,13 +287,15 @@ type Hooks interface {
 	ConfigurationWillBeSaved(newCfg *model.Config) (*model.Config, error)
 
 	// NotificationWillBePushed is invoked before a push notification is sent to the push
-	// notification server. The intention is to allow plugins to cancel a push notification.
+	// notification server.
 	//
-	// To cancel a push notification, return true.
+	// To reject a notification, return an non-empty string describing why the notification was rejected.
+	// To modify the notification, return the replacement, non-nil *model.PushNotification and an empty string.
+	// To allow the notification without modification, return a nil *model.PushNotification and an empty string.
 	//
-	// Note that this method will be called for push notification sent by plugins, including
-	// the plugin that created the push notification.
+	// Note that this method will be called for push notifications created by plugins, including the plugin that
+	// created the notification.
 	//
 	// Minimum server version: 9.0
-	NotificationWillBePushed(pushNotification *model.PluginPushNotification) (cancel bool)
+	NotificationWillBePushed(pushNotification *model.PushNotification, userID string) (*model.PushNotification, string)
 }