Should we consider replacing Google Groups (https://groups.google.com/g/nsubstitute) with GitHub discussions? (for example: https://github.com/xunit/xunit/discussions)

Because:

• I found a link to the Google Groups on the docs https://nsubstitute.github.io/help/return-for-all/ - but it isn't linked for the readme. (See https://github.com/search?q=repo%3Ansubstitute%2FNSubstitute%20groups.google.com&type=code)
• There is some spam there:
  
• We could convert between issues and discussion easier
• I prefer not using Google when not needed

Proposal:

• Enable GitHub discussions for this repo
• Move relevant parts
• Update the links on nsubstitute.github.io
• Remove the Google Groups