Test notary targets/delegation key rotation

The rotation of delegation and targets keys needs to be tested and the upload_to_harbor.py script should be updated to use the rotated keys when necessary.

Right now the initialize-gun.sh script can fail after setting up the necessary key infra for the pipeline to work, but before the targets key has been stored in vault. We may need to review and add any missing targets keys as well as improve the script logic to clean up all the infra if any piece fails.