fix(p2p-upgrades): Rate-limit requests to list installers from other devices

[gmaclennan]

Currently, discovery makes a lookup() request every 2 seconds, and when a peer event is emitted, it will make a GET /installers request to list the available installers. Theoretically this means that the GET /installers request happens once every 2 seconds, but in testing it appears that the peer event can be emitted more frequently than every 2 seconds, perhaps because other announce() events from other devices can also trigger a peer event. This can result in a saturation of GET /installers requests.

Fix: Rate-limit (throttle) requests to GET /installers by peer (e.g. requests to each peer should be throttled independently).