[feat] engines: add pixabay for royalty free images/videos

What's changed?
- this PR adds Pixabay, a collection of royalty free images
- additionaly it seems to have some videos, so there's an engine for it too

Author Notes
- when using SearXNG's transport, all our requests will get blocked, probably due to fingerprinting
- we should find an alternative solution because this is just a hacky change to make things work for now, but idk how ...

searx/settings.yml

@@ -1583,6 +1583,20 @@ engines:
     url: https://thepiratebay.org/
     timeout: 3.0
 
+  - name: pixabay images
+    engine: pixabay
+    pixabay_type: images
+    categories: images
+    shortcut: pixi
+    disabled: true
+
+  - name: pixabay videos
+    engine: pixabay
+    pixabay_type: videos
+    categories: videos
+    shortcut: pixv
+    disabled: true
+
   - name: pixiv
     shortcut: pv
     engine: pixiv