[feat] engine: implementation of https://hex.pm

The package manager for the Erlang ecosystem Find packages.

Co-authored-by: Bnyro <82752168+Bnyro@users.noreply.github.com>

searx/settings.yml

@@ -926,6 +926,11 @@ engines:
     shortcut: hn
     disabled: true
 
+  - name: hex
+    engine: hex
+    shortcut: hex
+    disabled: true
+
   - name: hoogle
     engine: xpath
     search_url: https://hoogle.haskell.org/?hoogle={query}