Publish framework and gui to GPR

[hlxid]

Description

With prealpha 3 we started to publish the API to GitHub Package Registry to allow developing plugins with build systems other than sbt.

In order to be able to embed Chat Overflow into other applications we additionally need to publish the framework and gui. Also having a download link for single jars is also quite handy instead of downloading and unzipping a complete deployment if you only want to get one specific jar.

This should also be automated using GitHub Actions. This way it only requires one time setup of the Action and doesn't add any overhead to the release process.

References

API publishing was introduced with #130.
Automation of API publishing is included in #134.
Requires #160 for gui publishing (done).
Enhancement request on discord.