Ability to set a policy about maximum expiry time

[simonw]

Inspired by my comment here: https://news.ycombinator.com/item?id=40190113

I just found this roadmap item relating to this: github/roadmap#599 - "Fine-grained PAT expiry policies for organizations"

It talks about letting organizations set a policy saying "no token lasts more than X months" - I'd love it if this could expand to "... or set a policy that says unlimited tokens are allowed", since then I could set that for my own organizations and stop complaining about this!

Even though I don't like forced-expiry, it's reasonable that some organizations would want that feature. So add it as a setting.

[simonw]

This may need to tie into a mechanism for modifying settings like this at runtime, since I want this as a user-facing admin setting for Datasette Cloud.