docs - add jquery extension to fix rtd theme

The Read the Docs theme for sphinx relies on jQuery in a few spots. It
looks like we already have a sphinxcontrib-jquery but weren't
referencing it as an extension in conf.py.

Adding this seems more "workaround" than fix - it may be worth following
the related upstream issue or monkeypatching our way around jQuery in
c7n-sphinxext.

See also: readthedocs/sphinx_rtd_theme#1546

docs/source/conf.py

@@ -36,7 +36,8 @@
     'sphinx.ext.viewcode',
     'c7n_sphinxext.docgen',
     'myst_parser',
-    'sphinx_markdown_tables'
+    'sphinx_markdown_tables',
+    'sphinxcontrib.jquery',
 ]
 
 # Extract only a classes docstrings