Adding a Hubspot provider for Goth

[justinrsweeney]

This adds Hubspot as a Goth provider: https://developers.hubspot.com/docs/api/working-with-oauth.

[justinrsweeney]

@techknowlogick Looks like the test failure here is related to building with Go 1.16 and upgrading to 1.17 would resolve the issue. It seems to be unrelated to the specific changes here, curious if you have a suggestion on how to proceed?

[techknowlogick]

Thanks @justinrsweeney, I've just bumped the min version to 1.18. could you merge in the recent changes to your branch so it can run again?

[justinrsweeney]

Thanks, updated from the recent changes.