feat(identity): migrate from OAuth 2.0 plugin to Kong Identity authorization servers and OIDC

[juliamrch]

Description

Work in progress, needs to be formatted and written, this PR only contains the workflow that works.

• Test on-prem
• Run the workflow
• Write the page
• Add versioning warnings and options
• Create script on-prem setup for reviewers

closes #3462

Preview Links

/identity/migrate-oauth-to-identity

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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