Configure publishing on tag

[propensive]

We should publish a new release of each library to Sonatype (or alternatively to GitHub) whenever a version is tagged. This should be possible using Irk's publish command, though it has not been widely tested, and has very little error handling.

One way this could work is to have a GitHub action which matches on "pending" tags, e.g. v1.0.4-pending and runs the build/publish script, then removes the v1.0.4-pending tag and adds v1.0.4 to the same commit. This would help to reduce the risk of repeated publishing attempts The script should also automatically ignore/delete v<x>-pending tags if a corresponding v<x> tag already exists, since its existence means that the release has already been published: it's likely that git push --tags would happen occasionally by accident, and we would want to avoid doing multiple releases.

[propensive]

Every library is now configured to run a publish workflow when its tagged with pending/<some version>, and will replace that tag with release/<some version> in the process. The publish workflow itself does nothing at the moment... that work still needs to be done in Irk, but we're a step closer.