Make new domain invitations expire after a period of time

[h-m-f-t]

Issue description

Domain invitations should be temporary, but right now they are long-lasting: they don't actually expire, and they exist until someone deletes, cancels, or retrieves them. Let's change that.

Implementation shouldn't be retroactive; this issue shouldn't make outstanding invitations inert. We should communicate the change to the nature of invitations to users.

Acceptance criteria

• Invitations have an "expired" state
• All new invitations expire after 30 days (existing invitations should be left alone)
• Content is updated in-registrar, in invitation emails, and on get.gov
• New content is created to guide a user to know what to do when they click on an expired invitation

Additional context

The new content for an expired invitation will have to be on manage.get.gov and presented after a user signs in with a Login.gov account.

Links to other issues

No response

[h-m-f-t]

We discussed this in team workshop; notes.