Render OpenAPI Spec of Admin APIs and Control APIs

[juzhiyuan]

Description

So far, the APISIX Admin APIs and Control APIs are hosted at https://apisix.apache.org/docs/apisix/admin-api/ using Markdown. To enhance the experience, an OpenAPI Spec render page would be much better.

Note: This change applies starting with APISIX v3.13; previous versions will continue to use the markdown format.

TODO

• Which OpenAPI Render Library to use?
• Build & Upload OpenAPI Spec files to apache/apisix repo.
• Delete Markdown contents. (Admin API and Control API)
• Use OpenAPI Render Library to render specs.