[develop]: Update doc requirements and add logo

[gspetro-NOAA]

DESCRIPTION OF CHANGES:

• Specify a minimum version of Sphinx in requirements.in
• Update requirements.txt based on requirements.in for a full list of dependencies. This will ensure uniform documentation builds across platforms.
• Add UFS logo to documentation.
• Rename docs directory to doc for NCO compliance.
• Slightly darken blue sidebar background to meet WCAG AA text/background contrast standards for large text.

NOTE: Most file changes are just a rename. Changes that need reviewing appear in: conf.py, requirements.txt, conf.py, .readthedocs.yaml, and theme_overrides.css

Type of change

• This change requires a documentation update

TESTS CONDUCTED:

None required. Documentation for PR can be viewed at the bottom of the PR.

DEPENDENCIES:

Merge PR #1014 first.

DOCUMENTATION:

All documentation.

ISSUE:

Resolves Issue #1017 .

CHECKLIST

• My code follows the style guidelines in the Contributor's Guide
• I have performed a self-review of my own code using the Code Reviewer's Guide
• I have commented my code, particularly in hard-to-understand areas
• My changes need updates to the documentation. I have made corresponding changes to the documentation
• My changes do not require updates to the documentation (explain). - N/A
• My changes generate no new warnings
• New and existing tests pass with my changes - N/A
• Any dependent changes have been merged and published

CONTRIBUTORS (optional):

[MichaelLueken]

@gspetro-NOAA - These changes look good to me! The new logo in RTD looks good and the modification to the background color really makes it pop!

It looks like there is a conflict with the ConfigWorkflow.rst following the latest merge. At your earliest convenience, please merge the latest HEAD into your text/rtd-update branch and I will be able to merge this back to develop. Thanks!