Add tools/signing/do-all-signing script, and other signing scripts improvements

After #40414 (closed), I think it would be nice to add a do-all-signing script. Currently we need to manually start each signing step, which requires spending a lot of time on a computer monitoring the progress of each signing step. A do-all-signing script could ask for all necessary passwords at the beginning, and then do all the signing steps without manual intervention. So we could for example start the script at night before sleeping, and the next morning all the signing is done.