ci: Automate patch releases and pre-releases

This work by automatically pushing a new tag on main and release
branches after each commit. The tag will be "devel" on main and the
version from postgrest.cabal for release branches. The release
workflow then runs as a tag pipeline, making the actual release.

For release branches, the tag will only be created if a tag for this
version doesn't exist, yet. This means to actually make a new patch
release, we still need to bump the version in postgrest.cabal. We
can automate this later as part of our backport-bot.

Resolves #2006
Resolves #2997

.github/actions/artifact-from-cirrus/action.yaml

@@ -101,8 +101,15 @@ runs:
         }
         archive="$(mktemp)"
         artifacts="$(mktemp -d)"
-        curl --no-progress-meter --fail -o "${archive}" \
-          "https://api.cirrus-ci.com/v1/artifact/task/$(get_external_id)/${{ inputs.download }}.zip"
+        until curl --no-progress-meter --fail -o "${archive}" \
+                "https://api.cirrus-ci.com/v1/artifact/task/$(get_external_id)/${{ inputs.download }}.zip"
+        do
+          # This happens when a tag is pushed on the same commit. In this case the
+          # job is immediately marked as "completed" for us, so we end up here after a few
+          # seconds - but the actual Cirrus CI task is still running and didn't produce its artifact, yet.
+          echo "Artifact not found on Cirrus CI, yet. Waiting..."
+          sleep 30
+        done
         unzip "${archive}" -d "${artifacts}"
         echo "artifacts=${artifacts}" >> "$GITHUB_OUTPUT"
     - name: Save artifact to GitHub Actions