weekly builder: Add option to exclude packages from spack.yaml

[AlexanderRichert-NOAA]

Description

This PR adds an option to provide $PACKAGES_TO_EXCLUDE in the weekly build scripts (03_SetupEnv.sh). If set, spack remove $PACKAGES_TO_EXCLUDE will be run. The motivation for this is to be able to run the weekly builds for a subset of the unified env while still using the unified-dev template.

Dependencies

none

Issues addressed

none

Applications affected

n/a

Systems affected

all

Testing

• CI: Note whether the automatic tests (GitHub actions tests that run automatically for every commit) pass or not
  • GitHub actions CI tests pass
  • GitHub actions CI tests do not pass (provide explanation)
  • GitHub actions CI tests skipped (provide explanation if necessary)
• Additional testing: Add information on any additional tests conducted
  • tested on Acorn

Checklist

• This PR addresses one issue/problem/enhancement or has a very good reason for not doing so.
• These changes have been tested on the affected systems and applications.
• All dependency PRs/issues have been resolved and this PR can be merged.
• All necessary updates to the documentation (spack-stack wiki) will be made when this PR is merged

[climbfuji]

I'll merge this after #1922 w/o retesting, since the weekly build scripts aren't used in CI.