Feature 1449 v4.1.0 beta6

[jprestop]

Pull Request Testing

• Describe testing already performed for these changes:
  
  Reviewed the release notes for beta6 here:
  https://metplus.readthedocs.io/en/feature_1449_v4.1.0-beta6/Users_Guide/release-notes.html#metplus-version-4-1-0-beta6-release-notes-2022-02-18

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  
  George had already added most of these. Only one was missing which was "Remove support for PB2NC_OBS_PREPBUFR_MAP (#1431)". I added that under "Enhancements" but am not sure that is really the best category, however, it seemed more appropriate than any other category we had. Is this acceptable or should there be a new category and what should it be called? Also, I could use some help with suggestions on what should be bolded.

• 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? [N/A]

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

• Please complete this pull request review by [ASAP].
  

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[jprestop]

@georgemccabe already added most all of the issues in the release notes. I corresponded with @JohnHalleyGotway via Slack about what to bold and about the placement of "Remove support for PB2NC_OBS_PREPBUFR_MAP". Once the tests finish running, I will go ahead and squash and merge.