Extending EmailHandler for Gmail and Microsoft OAuth2

[fiammybe]

GMail and Outlook are pushing us to stronger authentication. Where an App password was still possible until recently, both providers are now blocking that way of interacting, making it impossible to use a Gmail or Outlook mail address as your 'from' address for ImpressCMS communcations.

[fiammybe]

this can be done after the minimal composer integration, because we need external libraries