Introduce API for Oauth2 (non-OIDC) Support - 1.12 Backport

[inFocus7]

Backport of #7017

Checklist:

• [X] I included a concise, user-facing changelog (for details, see https://github.com/solo-io/go-utils/tree/master/changelogutils) which references the issue that is resolved.
• [X] If I updated APIs (our protos) or helm values, I ran make -B install-go-tools generated-code to ensure there will be no code diff
• [X] I followed guidelines laid out in the Gloo Edge contribution guide
• [X] I opened a draft PR or added the work in progress label if my PR is not ready for review
• [X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [X] I have made corresponding changes to the documentation
• [ ] ~~I have added tests that prove my fix is effective or that my feature works~~

[solo-changelog-bot[bot]]

Issues linked to changelog: https://github.com/solo-io/gloo/issues/6985

[inFocus7]

marking as work in progress while adding goleak updates here, but ready for review to check all passes CI

[sam-heilbron]

/kick https://storage.googleapis.com/solo-public-build-logs/logs.html?buildid=a252fc3d-2f13-4ce6-a7e3-4e4e784c5370

retry exhaused?