ci: add automated release workflow

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I don't see one. We should add one.
I can steal from the many other projects I've done this on.
As per the clj-commons team preference, should be triggered by the push of a release tag.

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Before being adopted by clj-commons, I think the pomegranate release was manually created (i.e. from developer's computer) using Clojure Core team's build.pom support. So via mvn commands.

After clj-commons adoption, it seems like a release is manually created via depstar and deployed via deps-deploy.

I'll switch us over to tools.build, automate and document.

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Also, the released pom seems to be pointing to HEAD, I'll make sure it instead points to the git commit of the release.

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Closed by PR #160