Enable dark mode switch on docs (#3977)

Author: rikatz

mkdocs.yml

@@ -27,7 +27,16 @@ theme:
     - navigation.top
     - navigation.expand
   palette:
-    primary: custom
+    - scheme: default
+      primary: custom
+      toggle:
+        icon: material/brightness-7
+        name: Switch to dark mode
+    - scheme: slate
+      primary: custom
+      toggle:
+        icon: material/brightness-4
+        name: Switch to light mode
   custom_dir: site-src/overrides
 edit_uri: edit/main/site-src/
 plugins: