Improve the "No mailbox" experience #277
Description
When OIDC connecting without a mailbox, there are 2 cases :
- OIDC_CREATE_USER=False, in this case we're redirected to the homepage without any message or hint.
- OIDC_CREATE_USER=True, we land on a page that could be improved : remove the search box, and add an env var to add a custom HTML message (Could be "please contact the administrator at XXX if you think you should have access to a mailbox")
