[API] Option to get access tokens with a quicker expiry

[afterlifepro]

Currently, I am debugging some issues with my token refreshing, and having to wait an hour or more before my code can be tested. A simple fix to this would be to simply add an `expires` field to the `https://accounts.spotify.com/api/token` endpoint, which overrides the default hour long expiry (ignored if > 3600 obviously)

This isn't a must have feature, but moreso a QOL feature to test token expiry time.

[Ximzend]

Hi @afterlifepro 

What is the exact issue with refreshing a token?

[afterlifepro]

The specific issue isn't important nor relevant as its specific to my codebase, however the fact that I have to wait at least an hour before I can get any feedback as to if my code works which is incredibly frustrating