Add github action "publish to github packages"

[dr0i]

By pushing to a "publish" branch this branch will be build and published to github packages.

• update README
• update build.gradle
• remove superflous task
• remove unused travis configs

See metafacture-fix#265.

[dr0i]

Todo: update documentation in the wiki.

[blackwinter]

This is great, thanks! But it should be published to the Metafacture registry, not your personal one.

[blackwinter]

👍

[fsteeg]

I'm a bit confused here. The version is feature-publish-SNAPSHOT (see package). Do we actually want an unspecific snapshot release? Even if we do, I don't think we'll be able to publish that version again, I think we'll have to (manually?) delete all the packages before we can publish again with the same version.

Before, I had it set up (not in master, I used these only for OERSI) to release only when we push to an RC branch, and use that simple branch name as the version. See 6613de9 (based on the original setup in 8d762ea). Resulting in versions like 5.3.3-rc2 (see package).

[blackwinter]

I'm a bit confused here. The version is feature-publish-SNAPSHOT (see package). Do we actually want an unspecific snapshot release?

TBH, I wasn't expecting this either, but it's a side effect of the "sophisticated" version logic in metafacture-core. My suggestion would be to drop it and simply rely on explicit version numbers (as in metafacture-fix).

[dr0i]

Thx @fsteeg , cherry-picked your solution.
Published metafacture-core-5.4.1-rc1 to GitHub packages.
See https://github.com/metafacture/metafacture-core/wiki/Maintainer-Guidelines#release-candidate how to do it.