Development dependency updates for next

[glennmatthews]

What's Changed

Trying to get ahead of the noise from #4564 and #4616. This updates all of the development (non-production) dependencies to their latest available versions; the only production dependency that this updates is Markdown because I got briefly confused and thought it was part of our docs dependencies. :-)

Some specific notes:

• For the Markdown dependency, I just broadened the range of acceptable versions (~3.3.7 -> >=3.3.7,<3.6.0) because we don't presently rely on any of the new features introduced in 3.4 or 3.5 versions of this library, so I figure there's no harm in accepting this range.
• I did not update mkdocs-include-markdown-plugin to latest (6.0.0) because as far as I can tell we actually don't use it anywhere in our docs since the restructuring in 2.0. Instead, I've removed it from mkdocs.yml and added a 3.0 TODO comment in pyproject.toml for us to remove the dependency entirely in the next major release.
• I added show_source: false to the mkdocstrings-python configuration in mkdocs.yml because there's no need to include the full source code to every class and function in the nautobot.apps namespace in the documentation, and it was making searches of the documentation really noisy/cluttered.
• I removed our custom Firefox configuration from nautobot/core/testing/integration.py because the browser_profile parameter that was supported in Selenium 3.x appears to have been quietly removed somewhere between Selenium 4.9 and 4.17. I did a little bit of searching but couldn't find an exact equivalent for configuring the browser under Selenium 4.x; I'm hoping that CI will show little-to-no performance impact of removing all of these config tweaks, but if it does show significant slowdown, I'll look into this further.

TODO

• Explanation of Change(s)
• Added change log fragment(s) (for more information see the documentation)
• n/a Attached Screenshots, Payload Example
• Unit, Integration Tests
• Documentation Updates (when adding/changing features)
• Example Plugin Updates (when adding/changing features)
• Outline Remaining Work, Constraints from Design

[HanlinMiao]

Should we have a .removed changelog fragment for this?

[glennmatthews]

Since it has no functional impact to the end user, I don't think so? Could add it to the .housekeeping if you like though. Note that the changes to the docs/requirements.txt files really only impact ReadTheDocs though.