Feature #2772 Apptainer documentation

[georgemccabe]

This PR also included a hotfix to change how quotation marks are added to plot_point_obs commands. Quotation marks are automatically applied for input files that are Python Embedding commands that contain spaces, so it is no longer necessary to add quotation marks in the PlotPointObs wrapper.

Pull Request Testing

• Describe testing already performed for these changes:
  

Ran commands from new instructions on casper

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  

• Review new content in documentation: https://metplus--2783.org.readthedocs.build/en/2783/Users_Guide/getting_started.html#metplus-in-apptainer
• Optionally, try to run commands on casper (must run module load apptainer first).

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes]

• Do these changes include sufficient testing updates? [Yes]

• Will this PR result in changes to the test suite? [No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Do these changes introduce new SonarQube findings? [No]
  
  If yes, please describe:

• Please complete this pull request review by 11/13/2024.
  

Pull Request Checklist

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[DanielAdriaansen]

I made some minor wording changes to the documentation, which I've suggested and request that @georgemccabe reviews and accepts those that you're in agreement with.

I followed the instructions on Casper, and was successful running the model_applications/pbl/PointStat_fcstHRRR_obsAMDAR_PBLH_PyEmbed.conf use case.

Thanks @georgemccabe, this will be a great addition!