Allow for token auth in invites and roles api

It seems that with current admin API it’s possible to invite users - but unfortunately, it’s not simple.
Even discarding the lack of documentation on admin/invites endpoint, the endpoint itself is pretty hard to use.

  1. It requires session authentication. If you try to use the JWT token auth, that is intended for integrations after all, you will get a 501 error with little indication as to what you did wrong. I spent far too long searching for any reason for request failure before I stumbled into a post here that said that it requires session auth.
  2. It needs a role id instead of a name - which I think will differ between each ghost instance, so you need to get it by using the admin/roles api endpoint, which once again needs session auth or it’ll return http 501.

I feel like even just allowing token auth for these endpoints would help with creating integrations that create users.

However, ideally I’d also like admin/invites to accept a role name instead of id - it’d allow to skip using api to find the role id, and since AFAIK you can’t create custom roles, and in the UI you select them by names anyway, so I don’t see a reason for having to use the id other than it possibly requiring a bit of work to add (so I understand if it’s not a priority for ghost team, but might be something that open source contributors can add)