Use multiple hackney pools

* federation (ap, salmon)
* media (rich media, media proxy)
* upload (uploader proxy)

Each "part" will stop fighting others ones -- a huge federation outbound
could before make the media proxy fail to checkout a connection in time.

splitted media and uploaded media for the good reason than an upload
pool will have all connections to the same host (the uploader upstream).
it also has a longer default retention period for connections.

lib/pleroma/web/rich_media/parser.ex

@@ -28,7 +28,7 @@ defmodule Pleroma.Web.RichMedia.Parser do
 
   defp parse_url(url) do
     try do
-      {:ok, %Tesla.Env{body: html}} = Pleroma.HTTP.get(url)
+      {:ok, %Tesla.Env{body: html}} = Pleroma.HTTP.get(url, [], pool: :media)
 
       html |> maybe_parse() |> get_parsed_data()
     rescue