Closes#416.
Workflows using x86_64-apple-darwin target with a `macos-13` runner
image have been migrated to `macos-15-intel` due to deprecation (see
#416), and `macos-14` images have been migrated to `macos-15`.
PR adds a nightly release pipeline.
Since the logic for the nightly build and release differs significantly
from the usual pipeline, I decided to put it in a separate file. The
same applies to the Python script that generates JSON files.
The nightly pipeline runs at 01:00 UTC every day, producing artefacts
and retaining them for 40 days if commits are made the day before it
runs.
cc https://github.com/paritytech/revive/issues/355
cc https://github.com/paritytech/devops/issues/4141
LJ