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/plugin_api_test.go

@@ -2266,13 +2266,22 @@ func TestSendPushNotification(t *testing.T) {
 			defer wg.Done()
 			post := th.CreatePost(th.BasicChannel)
 			post.Message = "started a conversation"
-			notification := &model.PluginPushNotification{
-				Post:    post,
-				Channel: th.BasicChannel,
-				UserID:  user.Id,
+			notification := &model.PushNotification{
+				Category:    model.CategoryCanReply,
+				Version:     model.PushMessageV2,
+				Type:        model.PushTypeMessage,
+				TeamId:      th.BasicChannel.TeamId,
+				ChannelId:   th.BasicChannel.Id,
+				PostId:      post.Id,
+				RootId:      post.RootId,
+				SenderId:    post.UserId,
+				SenderName:  "Sender Name",
+				PostType:    post.Type,
+				ChannelType: th.BasicChannel.Type,
+				Message:     "Custom message",
 			}
-			appErr := api.SendPluginPushNotification(notification)
-			require.NoError(t, appErr)
+			appErr := api.SendPushNotification(notification, user.Id)
+			require.Nil(t, appErr)
 		}(*data.user)
 	}
 	wg.Wait()
@@ -2286,7 +2295,7 @@ func TestSendPushNotification(t *testing.T) {
 		case model.PushTypeMessage:
 			numMessages++
 			assert.Equal(t, th.BasicChannel.Id, n.ChannelId)
-			assert.Equal(t, fmt.Sprintf("@%s: started a conversation", th.BasicUser.GetDisplayName(model.ShowUsername)), n.Message)
+			assert.Equal(t, "Custom message", n.Message)
 		default:
 			assert.Fail(t, "should not receive any other push notification types")
 		}