[python] Start move to {obs/var} specific arguments for get_anndata

[ivirshup]

Closes #1035

But needs discussion on API wrt upstream packages.

• [x] Merge main once #1150 is in to fix failing tests
• [x] Update docs

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.15%. Comparing base (39a5d1d) to head (b2c1860). Report is 24 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1149 +/- ## ========================================== - Coverage 91.16% 91.15% -0.02% ========================================== Files 77 77 Lines 5896 5910 +14 ========================================== + Hits 5375 5387 +12 - Misses 521 523 +2 ``` | [Flag](https://app.codecov.io/gh/chanzuckerberg/cellxgene-census/pull/1149/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=chanzuckerberg) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/chanzuckerberg/cellxgene-census/pull/1149/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=chanzuckerberg) | `91.15% <100.00%> (-0.02%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=chanzuckerberg#carryforward-flags-in-the-pull-request-comment) to find out more.

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[github-actions[bot]]

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[ivirshup]

Yep! Merging now.