[bug] Fix OIDC users requiring second approval

[tsmethurst]

This PR updates some of the OIDC logic in order to pre-approves users + accounts created via OIDC.

Rationale as follows:

// Since this user is created via oidc, which has been set up by the admin, we can assume that the account is already
// implicitly approved, and that the email address has already been verified: otherwise, we end up in situations where
// the admin first approves the user in OIDC, and then has to approve them again in GoToSocial, which doesn't make sense.
//
// In other words, if a user logs in via OIDC, they should be able to use their account straight away.

Closes https://github.com/superseriousbusiness/gotosocial/issues/357