Optimize workflows

[eugenschindler]

Currently, we have 3 workflows on main: build, publish packages, release.
Each of those flows builds everything from scratch. This can be optimized as follows:

• Build may not be necessary at all, if we can close the main branch for direct commits and enforce pull requests to be built and green before we can merge them. This depends on Find a way to protect main branch from direct commits #24.
• Given that build is not necessary on master, publish can take care of putting the relevant packages in the package repository.
• If we find a way to pass on which packages have to be released, the release also doesn't need to build from scratch and can simply put out relevant packages as a release.

Alternatively (since currently all three workflows get directly triggered upon any commit on main), we can combine build, publish packages, and release in one workflow (which is fine as long as we have the above described protection of main and pull request workflow). Finally, if we could relate the artifacts built by a pull request upon merging from that pull request, we could even optimize away the build step on the main workflow for publishPackages-release.