Credential protocol enhancement: OAuth token expiration and refresh tokens

[dscho]

Starting in Git 2.40, the protocol learned a few new keys including around storing and retrieving an OAuth token's expiration date. This will be helpful to support such that tokens stored in credential stores can be used or discarded without an extra network call to determine if they are still within the validity period. 

Likewise, the protocol from v2.41 now includes an optional OAuth refresh token key that allows helpers to more easily communicate both an access and refresh token as part of a get + store/erase request and response pair. Today, host providers have had to preemptively store the refresh token manually, in a separate credential store entry, even if the incorrect user account was selected.

Author: @mjcheetham

[crablab]

It's probably worth nothing the lack of support here does lead to problems with Forgjeo instances: https://codeberg.org/forgejo/forgejo/issues/2809