Add persistence diagrams for persistent homology analysis #1225

Description of feature

Hi, I have worked on persistent homology and persistence diagrams which have been a common technique used for extracting topological features for downstream analysis. I was wondering would you be interested if I added a few functions to squidpy which would allow this? Below is a small example.

Possible MVP:
sq.gr.persistent_homology(...) for computing persistence diagrams from adata.obsm["spatial"]
output stored in adata.uns[...] or returned as a tidy DataFrame
sq.pl.persistence_diagram(...) for visualization