ci: Import ci pipeline from original repo

When this repository was split from the original *dustin/sshca*
repository, the CI pipeline was not imported.  It wouldn't have mattered
if it had been, since it wouldn't have worked, anyway, given the path
changes.

ci/publish.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+. ci/common.sh
+
+buildah push "${IMAGE_NAME}:${TAG}" "${IMAGE_NAME}:${TAG}-${BUILD_NUMBER}"
+buildah push "${IMAGE_NAME}:${TAG}"
+case "${BRANCH_NAME}" in
+master|main)
+    buildah push "${IMAGE_NAME}:${TAG}" "${IMAGE_NAME}:latest"
+    ;;
+esac