Implement Patreon as an external provider

[millette]

- Do you want to request a feature or report a bug?
A feature. An addition to the list of supported providers

- What is the current behavior?
Current providers are very developer-centric

- What is the expected behavior?
Implement Patreon as an external provider, see https://docs.patreon.com/#oauth

[github-actions]

This issue has been automatically marked as stale because it has not had activity in 1 year. It will be closed in 7 days if no further activity occurs. Thanks!

[github-actions]

This issue was closed because it had no activity for over 1 year.