simple-repository-api: bump, explain api-version

[woodruffw]

See discussion in https://discuss.python.org/t/does-the-simple-repository-api-version-1-3-exist/79361 -- this updates the living index API spec to correctly reflect the latest API version (1.3), as well as add some callouts for the fields that make a response look like a 1.3 response (namely, provenance).

CC @di @brettcannon

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📚 Documentation preview 📚: https://python-packaging-user-guide--1803.org.readthedocs.build/en/1803/

[woodruffw]

NB: I didn't change it with this PR, but another possible improvement to this document is removing the "Additional Fields for the Simple API for Package Indexes" section and folding its contents into the relevant HTML/JSON sections, as needed. That should further reduce confusion, as that's the only section that mentions version 1.1 of the API.

(Another possible improvement is adding a "Version History" section, or maybe repurposing the "History" section to make the API version changes more explicit.)

[brettcannon]

another possible improvement to this document is removing the "Additional Fields for the Simple API for Package Indexes" section and folding its contents into the relevant HTML/JSON sections, as needed.

Yeah, probably being more explicit about what each version added would be good.

Another possible improvement is adding a "Version History" section

👍

[woodruffw]

Cool, I'll do that in a follow-up to keep things small here 🙂

[di]

(Approved but I am not actually an editor here, we will need one of @pypa/packaging-user-guide-editors to approve as well)

[woodruffw]

Gentle ping for merge now that this has been approved by @pypa/packaging-user-guide-editors!

[woodruffw]

Cool, I'll do that in a follow-up to keep things small here 🙂

Opened #1808 as the follow-up! There's even more I could do but I'm trying to keep each PR somewhat small for easy review.