Try token attr fix for compute engine service account

[lucienfregosibodyguard]

Add method + refresh credentials to get the token

Closes #92

Checklist

• This pull request references any related issue by including "Closes #<ISSUE_NUMBER>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• This pull request includes tests or only affects documentation.
• Summarized PR's changes in CHANGELOG.md

[desertaxle]

Thanks for the contribution @lucienfregosibodyguard! It looks like some of the tests need to be updated to account for the changes in this PR. Also, would you be able to add an entry to the changelog describing these changes?

[ahuang11]

Thanks for looking into this and making a PR! Looking at the changes, I realized we already have a built-in method for this on GcpCredentials. I think we should call it, but it's currently async so I made it sync compatible here.

Also, we might want to decorate get_configs here with @sync_compatible too and call await self_copy.credentials.get_access_token().

Let me know if that makes sense!

[lucienfregosibodyguard]

@ahuang11 it totally makes sense you can close this PR then and use only the original one

Can't wait to have this merged

[ahuang11]

Sure; I'll first merge this PR into mine so you're part of the contributors. Thanks again!