Auto-update list of custom connector when new files are added or updated.

[monty241]

Currently, Power BI evaluates once (at start time) what custom connectors are available by inspecting the folder.

During development, you will often re-deploy an existing product or add another one.

It would speed development cycles up when Power BI had a file system watcher on the folder and chose to reload the list of available custom connectors a few seconds after the contents changed. In that case, already running cases of the custom connectors could be killed without saving state.