Add support for Client Credentials flow

[dancrumb]

Is your feature request related to a problem? Please describe.

I'd like to be able to authenticate via client credentials in the Altair client

Describe the solution you'd like

Really, I'm looking for an update to the OAuth 2.0 Grant type options to include Client Credentials.

It would take the Client ID, Client Secret and Token URLs, with optional (or required, if you prefer) Scope.

Describe alternatives you've considered

There's no other alternative, beyond me sending my own request via cURL and then using the Bearer token Auth option

Additional context

No. I'm happy to add further context, if needed, but I think this one is probably fairly self explantory.