disable forced token expiry

Forcing token expiry at a year doesn't seem to gain us much, but does impose an intermittent maintenance burden when tokens expire and have to be rotated, storage updated, etc.

This changes the setting both for personal access tokens and for "service accounts".

Docs / background:

• https://docs.gitlab.com/administration/settings/account_and_limit_settings/#require-expiration-dates-for-new-access-tokens
• https://docs.gitlab.com/api/settings/

Bug: T385930

Closes T385930