Document how to set up social and OAuth login flows

## What

“how do I set up social/OAuth login flows?” questions. Close as Duplicate of the older thread if the answer is the same docs.

## Want

- “how do I set up social/OAuth login flows?” questions
- Close as Duplicate of the older thread if the answer is the same docs

## Ideas this came from

- [#8145 Setup flows for social login](https://github.com/goauthentik/authentik/issues/8145) — We are trying to login to our SPA application ( .net + react ) using authentik as wrapper for GCP project. How should authentication / authorization / enrollmen
- [#12200 setup social login](https://github.com/goauthentik/authentik/issues/12200) — What I want I'm trying to setup a login with an external oAuth source. What I have done 1. In Federation and Social Login created the oAuth Source 2. In the def

Start by reviewing the questions and proposed duplicate threads #8145 and #12200, then locate the existing documentation covering social and OAuth login flows. Document the setup path and compare it with those threads; done means recurring questions can be answered by the documentation or closed as duplicates.

Written by the indexing model from the issue text.