[feat] engines: add uxwing engine for icons (#4819)

- uxwing provides attribution-free icons to use for design projects
- svgrepo was my go-to before, but it's ratelimiting a lot recently

searx/settings.yml

@@ -2522,6 +2522,11 @@ engines:
     engine: tootfinder
     shortcut: toot
 
+  - name: uxwing
+    engine: uxwing
+    shortcut: ux
+    disabled: true
+
   - name: voidlinux
     engine: voidlinux
     shortcut: void