MM-22845: Added support for permalink previews. (#17796)

* MM-22845: Added support for permalink previews.

* MM-22845: Adds license to new file.

* MM-22845: Adds endpoint to retrieve multiple posts by id.

* MM-22845: Fix for deleted post.

* MM-22845: Adds config setting for permalink previews.

* MM-22845: Adds API test for new endpoint.

* MM-22845: Fix typo.

* MM-22845: Tests that post create or updated via App get the previewed_post prop.

* MM-22845: Tests for matching permalinks.

* MM-22845: Adds PreparePostForClient test for permalink previews.

* MM-22845: Embeds entire post in permalink metadata.

* MM-22845: Filter WS message payload of created and edited post based on permissions.

* MM-22845: Runs app layer generator.

* MM-22845: Lint check fix.

* MM-22845: Adds feature flag.

* MM-22845: Clones WS message.

* MM-22845: Removes knowledge of permalink from LinkMetadata table. Removes knowledge of user id from post embedding methods in favour of a 'sanitize' method/step.

* MM-22845: Handle nil post metadata.

* MM-22845: Switch to cloning post.

* MM-22845: Removes unused code.

* MM-22845: Refactor.

* MM-22845: Reverts whitespace change.

* MM-22845: Removes unnecessary code.

* MM-22845: Removes unnecessary function.

* MM-22845: Warn but don't error if permalinked referenced post or channel is not found.

* MM-22845: Fix for clone method.

* MM-22845: Fix for clone method.

* MM-22845: Updates translations.

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/notification.go

@@ -469,7 +469,13 @@ func (a *App) SendNotifications(post *model.Post, team *model.Team, channel *mod
 		message.Add("mentions", model.ArrayToJson(mentionedUsersList))
 	}
 
-	a.Publish(message)
+	published, err := a.publishWebsocketEventForPermalinkPost(post, message)
+	if err != nil {
+		return nil, err
+	}
+	if !published {
+		a.Publish(message)
+	}
 
 	// If this is a reply in a thread, notify participants
 	if a.Config().FeatureFlags.CollapsedThreads && *a.Config().ServiceSettings.CollapsedThreads != model.CollapsedThreadsDisabled && post.RootId != "" {
@@ -502,6 +508,18 @@ func (a *App) SendNotifications(post *model.Post, team *model.Team, channel *mod
 				if userThread != nil {
 					a.sanitizeProfiles(userThread.Participants, false)
 					userThread.Post.SanitizeProps()
+
+					previewPost := post.GetPreviewPost()
+					if previewPost != nil {
+						previewedChannel, err := a.GetChannel(previewPost.Post.ChannelId)
+						if err != nil {
+							return nil, err
+						}
+						if previewedChannel != nil && !a.HasPermissionToReadChannel(uid, previewedChannel) {
+							userThread.Post.Metadata.Embeds[0].Data = nil
+						}
+					}
+
 					message.Add("thread", userThread.ToJson())
 					a.Publish(message)
 				}