scripts: use "invenio run --extra-files" to reload on "invenio.cfg" changes

Apparently, `flask run` has [a `--extra-files` parameter](https://flask.palletsprojects.com/en/1.1.x/cli/#watch-extra-files-with-the-reloader), which allows passing other files that could trigger a reload when changed. That would be very useful e.g. for reloading for changes done in `invenio.cfg`.

Not sure if this could actually be useful/applicable for the entire `var/instance` folder...

Locate the script or entry point that handles `invenio run`, and read how it invokes the Flask development server. Verify how `invenio.cfg` and possibly `var/instance` are passed as extra files, then run the development command and confirm that configuration edits trigger a reload.

Written by the indexing model from the issue text.