docs: Fix for missing jQuery (#2416)

As mentioned in discord, the current build of the docs loses jQuery
functionality. This is due to sphinx being upgraded to version 6 in
which they removed jQuery and created a stand-alone package for it.

Additionally, in the process of doing that, I noticed the previously
mentioned fix (in the comments) for the `melos doc-setup` about removing
the single quotes to keep it clean didn't make into the final code. I
have updated that as it was previously confirmed to work on all
platforms in: https://github.com/flame-engine/flame/pull/2401

I noticed that the copyright that was in the `conf.py` was locked at
2021 and so I made it go to 2023 as well. This can be removed if not
desired, but thought maybe this had just been overlooked.

Finally, there was an error regarding a duplicate instantiation of a
constant. This had to do with the fact the basic theme provided with
sphinx, the next version after which the docs were based, had a bug fix
implemented:
https://www.sphinx-doc.org/en/master/changes.html#release-5-1-0-released-jul-24-2022.
In their fix, it also broke the way the flames theme works. On a side
note, the docs are using a very outdated version of the basic theme and
should likely be overhauled, but that is outside the scope of this pr.
None the less, after I finally figured out how the basic theme is
inherited and where that lived on my machine, I was able to resolve the
discrepancies and eliminate the conflicting names between the two
themes.

In short, all errors have been resolved and I have confirmed that
mobile, web, search, highlighting, menus, etc. all work - at least on my
machine.

doc/_sphinx/conf.py

@@ -36,6 +36,7 @@ extensions = [
     'extensions.flutter_app',
     'extensions.package',
     'extensions.yarn_lexer',
+    'sphinxcontrib.jquery',
 ]
 
 # Configuration options for MyST: