Log gateway resolution times

[autonome]

Currently we're still experiencing very long times for loading content from gateway.

Companion has a unique view - it can see from the user POV when an IPFS URL is entered, to the time the content is finally loaded.

We should log these, even if not expose in UI anywhere, so that we can view for development purposes how it changes over time.

This could be a log, or even be a simple median load time for all gateway requests might be interesting.

Eventually if we had metrics to Companion, we could report this info for an anonymized view of gateway performance across all installs.

[lidel]

What metrics would be useful to track?
While webRequest API still exists (#666 😈), it provides hooks for different stages of each request:

I am worried about logging every IPFS URL, but we could start with gathering content-agnostic data:

• Gateway URL (just Origin, no path) + Content-Length + time between each stage
  • Content-Length should help us normalize time against the size of requested data

Thoughts? Anything to add?