[feat] engines: add chatnoir general engine (#6183)

Chatnoir is an open source search engine developed by universities, based on
CommonCrawl (and others).  It's uncommented by default - we don't want to
overload the universities with bot traffic that targets SearXNG (sad truth why
we can't have nice things anymore)

searx/settings.yml

@@ -609,6 +609,12 @@ engines:
     shortcut: ca
     disabled: true
 
+  # - name: chatnoir
+  #   engine: chatnoir
+  #   shortcut: cha
+  #   search_index: cw22
+  #   disabled: true
+
   - name: chefkoch
     engine: chefkoch
     shortcut: chef