[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/plugin_api.go

@@ -665,7 +665,7 @@ func (api *PluginAPI) GetPostThread(postID string) (*model.PostList, *model.AppE
 }
 
 func (api *PluginAPI) GetPost(postID string) (*model.Post, *model.AppError) {
-	return api.app.GetSinglePost(postID)
+	return api.app.GetSinglePost(postID, false)
 }
 
 func (api *PluginAPI) GetPostsSince(channelID string, time int64) (*model.PostList, *model.AppError) {