Closes #2124

What was done

• Moved init of OAuth clients (google, github, discord and keycloak) to the SDK so users can also import them and use them
  • These clients are needed to refresh auth tokens
• Move some of the OAuth helpers to SDK - because they are only used in the SDK or could be useful for users
  • The env helpers are only used in the SDK
  • The redirect and one-time token helpers can be useful if users implement some OAuth client themselves
• Updated the OAuth tokens that we provide in auth hooks: we now provide all the data we get and not just the access token
  • We forward the data we receive so users will get the refresh token if we receive it

Left to do

• Update docs