Add script for gsi_pubsign build chaining target

Bug: 149803895
Test: ./gsi-pubsign-release.sh aosp_arm64 aosp_arm64_pubsign \
        aosp_arm64-artifact_path aosp_arm64_pubsign-artifact_path

Change-Id: I05e82f0605eec33c0da9b5a5d5cbf3506af3706c
1 file changed