ci: Upload non-SNAPSHOT releases to Sonatype

[langston-barrett]

As discussed in #11, we want to deploy releases to Sonatype, in addition to the Github releases page. I'm not familiar with this process, I imagine we'll need to add some credentials to the CI build (likely as secret environment variables) to make this work. There may be pre-built actions availble to help (https://github.com/marketplace/actions/nexus-repository-publisher-for-github-actions).

@tuxji said:

The second PR also will need to handle both snapshots (2.2.3-SNAPSHOT) and final releases (2.2.3) - only the latter kind will be copied to Maven central, so we will need to make final releases from time to time.