Upstreaming peerlog and time-to-first-byte metrics

[aschmahmann]

There are two metrics that Protocol Labs makes use of internally that are in this (historically named) branch of go-ipfs. It'd be great to upstream these metrics given that they've proven useful so far. We'll also be able to make that branch obsolete and make our release process a bit easier.

There are currently two commits on that branch to remove:

1. Peerlog - which logs all the peerIDs we see. We already have the peerlog plugin and we just enable it when building the Docker container in this commit.
   • If it's easy enough to make this configurable on the deployer/infrastructure side of things instead of as a commit modifying the docker build script that would be great
   • If not then we may want to consider bundling the plugin by default and triggering it via some config flag or environment variable
2. Time-to-First-Byte - It looks like this metric is already defined but not exposed without this commit. Perhaps @lanzafame can shed some light into the background here.