Bugfix #2412 develop climo

[JohnHalleyGotway]

These are the same code changes as PR #2420 to fix this issue in the main_v11.0 branch, but this adds 1 new test and tweaks the documentation slightly.

Expected Differences

• Do these changes introduce new tools, command line arguments, or configuration file options? [No]
  
  If yes, please describe:
  

• Do these changes modify the structure of existing or add new output data types (e.g. statistic line types or NetCDF variables)? [No]
  
  If yes, please describe:
  

Pull Request Testing

• Describe testing already performed for these changes:
  
  Manually ran the new Grid-Stat test to confirm that it works as expected and produced different output for different valid times.

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

• Confirm that the code changes match.

• Review the very minor doc addition.

• Inspect the newly created Grid-Stat output files to confirm that the SAL1L2 partial sums differ for different valid times and could use ncview to see that the gridded climo fields also change for different valid times.

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

• New Grid-Stat test in unit_climo_2.5deg.xml passes the same data in both the fcst/obs slots. And it processes the same TMP/P500 field 4 times but uses the set_attr_valid option to choose different valid times between Dec 15 and Jan 15 to demonstrate different types of time interpolation. In the output, you can see diffs in the SAL1L2 line type as well as the climo fields in the NetCDF matched pairs output files.

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

• Output from new test described above.

• Will this PR result in changes to the test suite? [Yes]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Please complete this pull request review by [Fri 1/27/23].
  

Pull Request Checklist

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[j-opatz]

The bulk of this PR's content was reviewed and approved in a previous feature branch that was made for the bugfix, so only the changes related to the newly added unit tests were reviewed.
These new unit tests demonstrate the updated temporal interpolation logic, and there is new output generated by them (although I wasn't able to check out what the results were: the /d1/projects/MET/MET_pull_requests/met-11.0.1/issue_2242/ area on Seneca had results that supported a correct output).
The updated documentation should also help users select the correct hour interval by providing an example that most users will encounter.