Theme option flyout to enable/disable theme's flyout (#1580)

* Theme option `flyout` to enable/disable theme's flyout

Add a theme option to enable/disable the theme's flyout integrated at the bottom
left into the navigation bar.

Closes #1579

* Use `flyout_display` with `hidden` and `attached` as options

* Make `hidden` as `flyout_display`

* Update docs/configuring.rst

Co-authored-by: Eric Holscher <25510+ericholscher@users.noreply.github.com>

---------

Co-authored-by: Eric Holscher <25510+ericholscher@users.noreply.github.com>

docs/configuring.rst

@@ -21,6 +21,7 @@ For example:
         'style_external_links': False,
         'vcs_pageview_mode': '',
         'style_nav_header_background': 'white',
+        'flyout_display': 'hidden',
         # Toc options
         'collapse_navigation': True,
         'sticky_navigation': True,
@@ -174,6 +175,16 @@ Miscellaneous options
     :type: string
     :default: ``#2980B9``
 
+.. confval:: flyout_display
+
+    Specify how to display the flyout (language and version selector).
+    This can be either ``attached`` or ``hidden``.
+    ``attached`` means that it will show the flyout in the bottom of the sidebar.
+    You will need to disable the default `Read the Docs flyout <https://docs.readthedocs.io/en/stable/flyout-menu.html>`_ in order to not have 2 flyouts showing.
+
+    :type: str
+    :default: ``hidden``
+
 
 File-wide metadata
 ==================

sphinx_rtd_theme/layout.html

@@ -67,7 +67,7 @@
     {%- endfor %}
     <script src="{{ pathto('_static/js/theme.js', 1) }}"></script>
 
-    {%- if READTHEDOCS %}
+    {%- if READTHEDOCS and theme_flyout_display != "hidden" %}
     <script src="{{ pathto('_static/js/versions.js', 1) }}"></script>
     {%- endif %}
 

sphinx_rtd_theme/theme.conf

@@ -18,3 +18,4 @@ prev_next_buttons_location = bottom
 style_external_links = False
 style_nav_header_background =
 vcs_pageview_mode =
+flyout_display = hidden