Bug 40763+40807: Add support for signing multiple browsers in tools/signing/nightly; Add config for basebrowser nightly signing

Merge Info

• Related Issues

  • Closes #40763 (closed)
  • Closes #40807 (closed)

• Backport Timeline

  • Immediate - patchsets for critical bug fixes or other major blocker (e.g. fixes for a 0-day exploit) OR patchsets with trivial changes which do not need testing (e.g. fixes for typos or fixes easily verified in a local developer build)
  • Next Minor Stable Release - patchset that needs to be verified in nightly before backport
  • Eventually - patchset that needs to be verified in alpha before backport
  • No Backport - patchset for the next major stable

• Issue Tracking

  • Link resolved issues with appropriate Release Prep issue for changelog generation

Change Description

I've been running the updated script on tbb-nightlies-master.tpo manually to check that there was no error. I also created the nssdb-basebrowser-1 certificate there, that we will use for signing base browser nightly updates.