Add option to add custom Provider

[bkeph]

Is your feature request related to a problem? Please describe.
I cannot connect to a SSO that is not present (and will not be) in the list

Describe the solution you'd like
I would like to connect a SSO of my choice by adding a provider constructed in the same way as the ones already present

Describe alternatives you've considered
I have tried adding my own provider, but I got stuck at redirecting to the SSO login page. After I click on the login with SSO button on the login page, I keep being redirected to the initial URL + /api/admin/oauth/authorization/specific-sso instead of the proper SSO login page. Probably that happens because adding a Provider for the specific SSO is not enough to make it work.

[sourabpramanik]

Not in the roadmap, but highly appreciate the contribution for the same