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

* add SendPushNotification plugin api method

* lint; add testing.Short bc of the sleep

* add interface and generated layers

* add fields to PluginPushNotification; generate mocks

* SendPushNotification -> SendPluginPushNotification; improved comments

* more comments; fix test

* send api.ctx

server/public/model/plugin_push_notification.go

@@ -4,9 +4,18 @@
 package model
 
 // PluginPushNotification is sent to the plugin when a push notification is going to be sent (via the
-// NotificationWillBePushed hook).
+// NotificationWillBePushed hook), and is used as the source data for the plugin api SendPluginPushNotification method.
+//
+// Note: Please keep in mind that Mattermost push notifications always refer to a specific post. Therefore, when used
+// as source data for `SendPluginPushNotification`, Post and Channel must be valid in order to create a correct
+// model.PushNotification.
+// Note: Post and Channel are pointers so that plugins using the NotificationWillBePushed hook will not need to query the
+// database on every push notification.
 type PluginPushNotification struct {
-	Post    *Post
-	Channel *Channel
-	UserID  string
+	Post               *Post    // The post that will be used as the source of the push notification.
+	Channel            *Channel // The channel that the post appeared in.
+	UserID             string   // The receiver of the push notification.
+	ExplicitMention    bool     // Used to construct the generic "@sender mentioned you" msg when `cfg.EmailSettings.PushNotificationContents` is not set to `full`
+	ChannelWideMention bool     // Used to construct the generic "@sender notified the channel" msg when `cfg.EmailSettings.PushNotificationContents` is not set to `full`
+	ReplyToThreadType  string   // Used to construct the generic CRT msgs when `cfg.EmailSettings.PushNotificationContents` is not set to `full`; see `App.getPushNotificationMessage` for details.
 }