Summary/Motivation:

This PR restructures the PyROS online documentation and adds a new tutorial to the documentation.

Changes proposed in this PR:

• Reorganize the PyROS online documentation and split it into multiple webpages
• Add a new, extensive tutorial to the PyROS online documentation
• Replace the original quickstart example problem with a problem that is smaller, easier to write down, and less sensitive to the subsolver(s) used (see this comment of #3649)
• Add the mathematical definition of each pre-implemented PyROS UncertaintySet class to the class's docstring

TODO (after #3732 merged)

• Account for changes to the logging system in the restructured online docs
• Rename the new PyROS doc folder as "pyros", and make the original PyROS reST file reference the main page of the new PyROS doc folder
• Update version number, changelog

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