Monitor invitations usage to determine if we need to automate cleanup

## Description
With the new [Self-serve ownership](https://github.com/cds-snc/platform-forms-client/pull/4392) feature, there is a new Invitations table in the database.
When an invitation is accepted or declined, the invitation record is deleted automatically.
Each invitation has an expiry date associated with it.
When an invitation expires, the database record remains until an owner either deletes (cancels) the invitation, or re-invites the user.

The question is, what to do about old/expired invitations not cleaned up by form owners, or more specifically, **if** we need to do anything.

This issue is just a reminder to check in from time to time on the usage of the Invitations feature, and see if there is an excess of old/expired invitations piling up that might need to be automatically cleaned up.