Use multiple hackney pools

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.