Documentation update for Chapter 5. Adding Test Packages (Chained Environment)

[natalie-perlin]

Description

Documentation changes for re-written and extended Chapter 5: Adding Test Packages (Chained Environment)

Dependencies

Issues addressed

Resolves issue: #1749

Applications affected

Documentation-only changes

Systems affected

List all systems intentionally or unintentionally affected by this PR.

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)
• New tests added: List and describe any new tests added to GitHub actions
  • ...
• Additional testing: Add information on any additional tests conducted
  • ...

Checklist

• This PR addresses one issue/problem/enhancement
• 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 on readthedocs are included in this PR
  • For site config updates, check in particular doc/source/PreConfiguredSites.rst and doc/source/MaintainersSection.rst
• All necessary updates to the spack-stack wiki will be made when this PR is merged

[climbfuji]

Thanks @natalie-perlin. I'll include those updates in the new documentation on the wiki. The readthedocs version will be removed starting with this release 2.0.0.

[climbfuji]

I've included this update in https://github.com/climbfuji/spack-stack/wiki/New-and-chained-environments-for-existing-sites.

This PR will be closed as unmerged once the wiki update is complete and the docs directory in spack-stack was removed (separate PR).

[natalie-perlin]

@climbfuji @AlexanderRichert-NOAA - thanks for the feedback!
Could these changes go to develop branch for the meanwhile (could submit as a separate ticket) that still 1.9.x-based?