Move API documentation from Warehouse developer docs to PyPI user docs

[di]

Documentation for our APIs and datasets currently lives in our developer-facing docs: https://warehouse.pypa.io/api-reference/index.html

However, these are really end-user docs, and should live at https://docs.pypi.org/ instead.

[woodruffw]

Adding a roadmap:

• [x] Index (#16398)
  • [x] Feeds: #17171
  • [x] JSON API: #17178
    • [x] Update links to the JSON API once migrated, e.g. in the integration guide docs: https://github.com/pypi/warehouse/pull/17211
  • [x] Legacy API: https://github.com/pypi/warehouse/pull/17123
  • [x] Stats API: #17161
  • [x] ~~XML-RPC (N/A?)~~
  • [x] Integration guide: https://github.com/pypi/warehouse/pull/17173
  • [x] BigQuery Datasets: #17162
  • [x] Integrity API (i.e. PEP 740, not currently documented): #16398

Once each of these is moved/added, it might make sense to add redirects from the old dev-docs URLs to the new user-docs ones.

[di]

XML-RPC (N/A?)

I think it would be wise to not bother porting these docs.

Integration guide (N/A?)

I think this can probably get included in the top-level page at https://docs.pypi.org/api/

[woodruffw]

All planned migrations are complete, so closing!

[di]

Should we add redirects from the old URLs?

[woodruffw]

Should we add redirects from the old URLs?

Yep! I was trying to figure out a good way to do that in Sphinx but couldn't find one (there's a lot of ways to redirect to a different Sphinx doc, but not an arbitrary URL). I'll do some more looking here.

[woodruffw]

https://documatt.com/sphinx-reredirects/usage.html might do the trick; I'll play around with that.

[woodruffw]

https://github.com/pypi/warehouse/pull/17213 has the redirects!