Python spec for geometry dataframe

[jp-dark]

Changes:

• Add a new GeometryDataFrame class
• Adds shapely as a somacore Python dependency.

WIP:

• How we want to handle the two-dimensional geometry index dimension for both schema specification needs further investigation.

Issues: Closes single-cell-data/TileDB-SOMA#2677

[jp-dark]

[sc-43829]

[pablo-gar]

I reviewed the naming of the introduced object and methods. I defer to others on the API review.