Feature 1667 doc conventions

Pull Request Testing

[x] Describe testing already performed for these changes:
This was a big undertaking. I added in all of the items from the original issue. But there were quite a few more topics to cover. See the section headers for all of the new items. Many of the items were pulled from "METplus Sphinx Documentation Guide". There were MANY different iterations of this work. They can be found in Lisa's personal directory, "2023 METplus Cont. Guide Overview and Conventions".
[x] Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
. Feel free to do a cursory check of https://metplus.readthedocs.io/en/feature_1667_doc_conventions/Contributors_Guide/documentation.html#underline section 10.2. It has been reviewed in detail. Once this is committed, I'd like to share this information at a METplus All Hands Meeting.
[x] Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes there are no warnings]
[x] Do these changes include sufficient testing updates? [No]
[x] Will this PR result in changes to the test suite? [No]
If yes, describe the new output and/or changes to the existing output:
[x] Please complete this pull request review by 11/3/23.

See the METplus Workflow for details.

[ ] Add any new Python packages to the METplus Components Python Requirements table.
[ ] Review the source issue metadata (required labels, projects, and milestone).
[ ] Complete the PR definition above.
[ ] Ensure the PR title matches the feature or bugfix branch name.
[ ] Define the PR metadata, as permissions allow. Select: Reviewer(s) Select: Organization level software support Project or Repository level development cycle Project Select: Milestone as the version that will include these changes
[ ] After submitting the PR, select the :gear: icon in the Development section of the right hand sidebar. Search for the issue that this PR will close and select it, if it is not already selected.
[ ] After the PR is approved, merge your changes. If permissions do not allow this, request that the reviewer do the merge.
[ ] Close the linked issue and delete your feature or bugfix branch from GitHub.