Change Sphinx theme and add Intersphinx for UI and Pyomo (#1350) #6191

Job	Run time
Compatibility tests	4m 16s
Check code formatting (Black)	29s
Check Spelling	6s
Build Sphinx docs	5m 24s
Pylint	4m 38s
pytest (py3.8/linux)	18m 37s
pytest (py3.8/win64)	18m 35s
pytest (py3.9/linux)	18m 40s
pytest (py3.9/win64)	18m 33s
pytest (py3.10/linux)	16m 44s
pytest (py3.10/win64)	18m 39s
pytest (py3.11/linux)	18m 43s
pytest (py3.11/win64)	18m 40s
pytest (py3.12/linux)	14m 59s
pytest (py3.12/win64)	18m 35s
Upload coverage report (Codecov)	1s
	3h 15m 39s

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