OpenAPI Generated Docs

[cipherboy]

Currently API docs are hand-maintained: https://github.com/openbao/openbao/tree/development/website/content/api-docs

This has lead to a divergence between them and the in-code docs at various points of time; while OpenBao uses a custom framework, it has the ability to generate an OpenAPI schema and thus should have the ability to generate OpenAPI docs, which would decrease the burden of accepting changes and increase maintainability of our documentation.

This needs to be done carefully as the hand-written docs and the OpenAPI docs will likely differ, so we'll likely want to go plugin-by-plugin and manually review and merge back any useful changes.

[JanMa]

I took a closer look into this, and as far as I can see a lot of the prerequisites are already in place. Using the gen_openapi.sh script and openapi generator we can already produce some pretty solid API docs.

What's still left to do is to adjust the default template of the document generator we choose to use with the openapi generator so it fits into the upcoming openbao website