Update the citations list

[jhlegarreta]

The citations list is probably missing works that have cited ITK (or tools in the ITK ecosystem, e.g. SimpleITK, etc.) in the recent years, as the current list's most recent reference is from 2020.

A quick search across search engines (general or publication-oriented) would help in this.

The following reference should be added to the citations list:
https://link.springer.com/article/10.1007/s00366-020-01040-9

And maybe this one should be added as well:
https://zenodo.org/record/8136801

[thewtex]

OpenSource.Science (OSSci) and CZI are working on citation mining with ITK support, we could add the results.