docs: describe why package.authors is deprecated

[AlexTMjugador]

What does this PR try to resolve?

Common sense and a range of research findings suggest that making the rationale behind a rule clear and agreeable improves compliance. Applying that observation to the package.authors deprecation notice in the Cargo package manifest format documentation, making the rationale for the deprecation more easily accessible should help people make more informed decisions about whether and how to migrate away from it.

Personally, until I decided to dig deeper into the matter, I have been considering tombi's warnings about package.authors being deprecated to be noisy lints without a clear reason or an obvious way forward that warranted addressing.

This change expands the package.authors deprecation notice to include a summary of the deprecation rationale stated in PR #15068, along with a link to the PR for anyone interested in learning more about the context behind the deprecation.

How to test and review this PR?

N/A

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[epage]

Note that #16458 is the issue for this and it hasn't been marked as S-accepted, meaning it isn't ready for a PR.

[AlexTMjugador]

Thanks for the pointer to that issue!

I must admit that I didn't look for issues reporting the lack of rationale for the deprecation before opening this PR because I expected most people to just ignore the lint as I have done before, but on the other hand, I feel validated that I was not the only one to find the lack of a deprecation rationale odd.

For now, I'll keep this PR open. If any decisions are made about the matter, feel free to merge it or let me know what needs tweaking. For what it's worth, I don't think my paragraph really qualifies as a "treaty", and the reasons it gives for the deprecation read extremely unlikely to change over time to me.

[epage]

If you want to leave this open, then I'll move this to draft status to make it clear for people going through the queue this blocked on the issue. As a warning, we may still end up closing it, always being able to re-open it later, to reduce the amount of content we are looking at.