[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>

api4/preference.go

@@ -110,7 +110,7 @@ func updatePreferences(c *Context, w http.ResponseWriter, r *http.Request) {
 
 	for _, pref := range preferences {
 		if pref.Category == model.PreferenceCategoryFlaggedPost {
-			post, err := c.App.GetSinglePost(pref.Name)
+			post, err := c.App.GetSinglePost(pref.Name, false)
 			if err != nil {
 				c.SetInvalidParam("preference.name")
 				return