docs: adds article for OAuth2 and OIDC disovery endpoints

[unatasha8]

Adding a new image for the Device Authorization Flow (content added in separate PR).

Related Issue or Design Document

DOC: OSS 25.4 Launch #9488

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• [x ] I have read the contributing guidelines and signed the CLA.
• [x ] I have referenced an issue containing the design document if my change introduces a new feature.
• [x ] I have read the security policy.
• [x ] I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact [email protected]) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

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