Port / Add Documentation for VarianceSample and VariancePopulation

[alamb]

Draft as it builds on #12747

Which issue does this PR close?

Part of #12740

Rationale for this change

Automatically generating documentation has several benefits as listed on #12740

What changes are included in this PR?

1. Port documentation

Are these changes tested?

Are there any user-facing changes?

[alamb]

I also used this PR as a way to double check the new CI check works -- here is an example of it failing: https://github.com/apache/datafusion/actions/runs/11166713917/job/31041794120?pr=12742

[comphead]

lgtm, thanks @alamb
@Omega359 I'm thinking if we can build the same doc from using rustdoc or rust attributes 🤔

[Omega359]

@Omega359 I'm thinking if we can build the same doc from using rustdoc or rust attributes 🤔

Absolutely we could, and I actually toyed with rustdoc approach at first. My main concern with that is that I envision this is useful outside of just the website documentation and for that I would believe we want the docs to be as easily accessible as possible. I can't think of more accessible ways to provide end-user type documentation than via api. It does mean of course that unless a way is found to incorporate this into the rustdoc it wouldn't show up in docs.rs which I admit is unfortunate.

[alamb]

@Omega359 I'm thinking if we can build the same doc from using rustdoc or rust attributes 🤔

Absolutely we could, and I actually toyed with rustdoc approach at first. My main concern with that is that I envision this is useful outside of just the website documentation and for that I would believe we want the docs to be as easily accessible as possible. I can't think of more accessible ways to provide end-user type documentation than via api. It does mean of course that unless a way is found to incorporate this into the rustdoc it wouldn't show up in docs.rs which I admit is unfortunate.

Maybe we can add something to the rust docs (via macro or something) that points do the website version.

Or we could perhaps make a similar script that would update the inlined rust documentation too (that might be getting too fancy 🤔 )

[alamb]

Thank you for the review @comphead