generate dfs in obsm and varm

[rcannood]

Description of feature

It's also possible to store data frames in obsm and varm:

import anndata as ad

adata = ad.AnnData(
  obs=pd.DataFrame(
    index=["a", "b", "c"],
  ),
  obsm={
    "df": pd.DataFrame(
      {
        "a": [1, 2, 3],
        "b": [4, 5, 6],
      },
      index=["a", "b", "c"],
    )
  },
)

Would it be possible to add these to the generators as well?

[LouiseDck]

Yes, Will do!
Related, I think we should also generate data frames in .uns as well, which we currently don't.