feat(aigw): Migrate OIDC

[cloudjumpercat]

Description

Fixes #6393

Preview Links

• (NEW page) /ai-gateway/openid-connect/
  • I opted to use includes with the OIDC plugin because it's using the OIDC plugin under the hood, it's not separate. But let me know if you think this approach is wrong.
  • From my research mTLS proof of possession and OAuth 2.0 (because there is no auth policy) aren't supported (source) so I've removed those
  • Verify that the include pages render the correct variables
• (updated) /ai-gateway/entities/ai-auth-strategy/
  • Updated a few sections based on research I did.
• /plugins/openid-connect/
  • Check this against https://developer.konghq.com/plugins/openid-connect/ to verify that everything looks the same
• Note: The includes should be the exact same as what is currently in the OIDC plugin overview, other than I've added variables for conditional rendering.
• Verify that this redirects to the new OIDC auth strategy page: /ai-gateway/policies/openid-connect/

Checklist

• Tested how-to docs. If not, note why here.
• All pages contain metadata.
• Any new docs link to existing docs.
• All autogenerated instructions render correctly (API, decK, Konnect, Kong Manager).
• Style guide (capitalized gateway entities, placeholder URLs) implemented correctly.
• Every page has a description entry in frontmatter.
• Add new pages to the product documentation index (if applicable).

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[cloudjumpercat]

Any idea how to get the schema to render? https://deploy-preview-7286--kongdeveloper.netlify.app/ai-gateway/openid-connect/#schema

Claude suggested this and it looks correct based on other AI entities. I just didn't want to link out to the OIDC plugin reference (although the case could be made for it since it is this plugin under the hood).