MM-11272 Added initial post metadata (#9175)

* MM-11272 Added app.PreparePostForClient

* MM-11272 Added app.PreparePostListForClient

* MM-11272 Added EmojiStore.GetMultipleByName

* MM-11272 Added emojis to PreparePostForClient

* MM-11272 Added unit tests for getting reaction counts

* MM-11272 Added unit tests for TestPreparePostForClient

* MM-11272 Added emojis from reactions to Post.Emojis

* MM-11272 Always update post.UpdateAt when reactions change to bust cache

* Fixed merge conflicts

* Moved post metadata-related code into its own file

* Update store mocks

* Fixed typo

* Add missing license headers

* Updated post metadata tests when custom emojis are disabled

* Fix unreliable unit tests

* Fix inconsistent casing in SQL statements

* Fix blank line

* Invalidate store cache after making changes

* Clear post cache synchronously with reactions

app/notification.go

@@ -317,8 +317,13 @@ func (a *App) SendNotifications(post *model.Post, team *model.Team, channel *mod
 		}
 	}
 
+	clientPost, err := a.PreparePostForClient(post)
+	if err != nil {
+		mlog.Error("Failed to prepare new post for client", mlog.Any("err", err))
+	}
+
 	message := model.NewWebSocketEvent(model.WEBSOCKET_EVENT_POSTED, "", post.ChannelId, "", nil)
-	message.Add("post", a.PostWithProxyAddedToImageURLs(post).ToJson())
+	message.Add("post", clientPost.ToJson())
 	message.Add("channel_type", channel.Type)
 	message.Add("channel_display_name", notification.GetChannelName(model.SHOW_USERNAME, ""))
 	message.Add("channel_name", channel.Name)