Add release gerber files GitHub Actions workflow

[carbncl]

This provides GitHub actions workflows that creates GitHub releases with automatically generated gerber files:

• Triggered when a version tag is pushed
• Releases are created as draft so you can edit the description before publishing it
• You can see a release example there: v2.1+20200808
• The gerber files are produced in a docker container with kicad-exports and use a kiplot configuration file (.kiplot.yml) that was written based on foostan kicad configuration and should be fine for a manufacturer such as JLCPCB
• Sadly, empty .sch files had to be added for plates because of a limitation of kicad-export

[foostan]

Thank you so much!
It's concept is good and it's helpful to release gerbers.

hmmm, but it's has some problems

• Currently I'm not use tag
• Corne keyboard has a many lineup so I can't release all at same timing
• I want release after prototyping and release it's gerber file so I'm not understand advantage of building a gerber on CI.

[carbncl]

• I thought you used tags, reason why I've setup the workflow to be triggered by them. But there are many other ways. Tag => release is a good logical choice I think, at least for software...
  • In my opinion, it would be nice to tag any version you do, with a changelog, even of a single lineup.
• You could split release lineups for instance by tagging cherry-v3 and removing unnecessary generated files before releasing the generated draft.
• CI in this case it just a way to ease things, and also guarantee that generation settings are consistent. But that is clearly not strongly required. Having Gerber files available for download would help people, especially the one that aren't experienced to KiCad.

[carbncl]

Also for prototyping you could use kiplot with that configuration, that would guarantee people to have the same setup as you.

[foostan]

Thank you for your suggestions. I’m with you.

• At first, cleanup a lot of files for each lineup
• I will try to management tags for each lineup
• I will try to use kiplot based on this PR

It may take some time because I'm prototyping new version of corne cherry.

[carbncl]

No hurry, do as you like. I'll let this open for now. Feel free to close, merge, cherry pick or whatever :)

[foostan]

I'm preparing new release so merge this PR.
After that I will try to management tags for each lineup.