[MM-42192] Include deleted posts in GetPost (#20358)

* Introduced include_deleted query param on get posts endpoint

* Update the correct func name in the comment.

Co-authored-by: santoniriccardo <santoni.riccardo@gmail.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/post_metadata.go

@@ -540,7 +540,7 @@ func (a *App) getLinkMetadata(requestURL string, timestamp int64, isNewPost bool
 	if looksLikeAPermalink(requestURL, a.GetSiteURL()) && *a.Config().ServiceSettings.EnablePermalinkPreviews && a.Config().FeatureFlags.PermalinkPreviews {
 		referencedPostID := requestURL[len(requestURL)-26:]
 
-		referencedPost, appErr := a.GetSinglePost(referencedPostID)
+		referencedPost, appErr := a.GetSinglePost(referencedPostID, false)
 		// TODO: Look into saving a value in the LinkMetadata.Data field to prevent perpetually re-querying for the deleted post.
 		if appErr != nil {
 			return nil, nil, nil, appErr