better release script (and overall updates)

[baronfel]

This updates:

• FAKE to .net 6 alphas
• Paket to latest
• adds versioning from the changelog
• updates FCS
• slims down the fake build script massively, relying on Directory.Build.props and the changelog to drive metadata
• adds a release github action that uses a nuget key (which I'll generate)

[baronfel]

Fixes #101

[baronfel]

final blocker before merge is that the Fornax package doesn't have @ionide as an owner. @Krzysztof-Cieslak can you change that so I can provision a key and merge?

[baronfel]

don't merge quite yet - doing a side-by-side diff with the generated packages in nuget.info shows a layout difference from 0.13.1

[baronfel]

content issue fixed - the template needs to be inside the packed tools dir, which is why the linkbase stuff was there before. this is now ready to gone once fornax package ownership is moved to the ionide org.

[baronfel]

fornax is moved to the ionide org, key is set in this repo's settings, now to merge, tag and verify the pipeline.