Periodically load broker metadata from configured URL

[joeribekker]

Storing the URL allows us to retrieve the broker metadata, as is done now. But, the intention of #45 was to also do this periodically in an automated way.

We could provide a Celery Beat task to do this every week. If it fails, report the error in Sentry but make sure nothing is changed. This saves us some helpdesk overhead. The task should then be added to the project using this library.

[sergei-maertens]

There is the update_stored_metadata management command, integrating that in a project through celery beat is the recommended approach here.