Migrate API to flask-restx

[nikromen]

Follow up from #1865

Migrate API_v3 to flask-restx and create documentation for it (models, parsers, docs, ...)

API endpoint namespaces TODO list:

• Migrate api_v3/build-chroots to flask-restx #3000
• Migrate api_v3/builds to flask-restx #2997
• Migrate api_v3/general to flask-restx #2999
• mock chroots (Convert tiny endpoints to flask-restx #2998)
• modules (Convert tiny endpoints to flask-restx #2998)
• monitor (Convert tiny endpoints to flask-restx #2998)
• packages (Finish last bits of api_v3/project-chroots && packages #2996)
• Migrate api_v3/permissions to flask-restx #3001
• project chroots (Finish last bits of api_v3/project-chroots && packages #2996)
• Migrate api_v3/projects to flask-restx #2995
• Migrate api_v3/rpmrepo to flask-restx #3002
• webhooks (Convert tiny endpoints to flask-restx #2998)

Other follow-ups:

• Use some common descriptions between Fask-restx fields and WTForms #3029
• Use I/O validation for flask-restx #3031

[cyqsimon]

I was trying to do some scripting just now, got to this page, and thought "there's zero ways in this world that there is no API for something as simple as listing out a project's packages."

Of course there was; I just had to directly look in the source code. So I did a search for issues and landed here.

I've actually had some experience working with OpenAPI in Rust (with utoipa). Not sure how (or if) this can be any help to this repo though.

[nikromen]

Thanks for the tip @cyqsimon. Yes, as you pointed out, we don't have fully documented our API at this point. We already researched which OpenAPI to migrate to but it will take a while since we write the documentation for all namespaces.