This PR implements a callaback that is executed on any SSO auth (registration and logins). This introduces an ability to add custom callbacks using ModuleAPI.

Reasoning:

• Password auth provider callbacks - will not work with SSO type logins;
• account_validity_callbacks.on_user_registration runs only on registration and is called before external_ids are set removing the ability to get the remote_user_id inside the ModuleAPI callback'
• There is not general on_login callback (which can be another interesting solution);

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
  • Feel free to credit yourself, by adding a sentence "Contributed by @github_username." or "Contributed by [Your Name]." to the end of the entry.
• Pull request includes a sign off
• Code style is correct
  (run the linters)

Signed-off-by: Andrii Yasynyshyn yasinishyn.a.n@gmail.com