Fetch preview requests through the MediaProxy. Separate connection options are not needed.

Use a separate pool for preview requests

config/config.exs

@@ -445,10 +445,7 @@ config :pleroma, :media_preview_proxy,
   enabled: false,
   thumbnail_max_width: 600,
   thumbnail_max_height: 600,
-  image_quality: 85,
-  proxy_opts: [
-    head_request_max_read_duration: 5_000
-  ]
+  image_quality: 85
 
 config :pleroma, :chat, enabled: true
 
@@ -761,6 +758,11 @@ config :pleroma, :pools,
     max_waiting: 10,
     timeout: 10_000
   ],
+  preview: [
+    size: 50,
+    max_waiting: 10,
+    timeout: 10_000
+  ],
   upload: [
     size: 25,
     max_waiting: 5,