Feature: Include route in simulation output

Add the option to include the route that a HTLC has taken in our simulation output (probably with an option to turn on/off so that it's not too noisy).

This isn't straightforward because right now we report per-payment (which may have multiple HTLCs), and just note a HTLC count. We'd need to re-examine the way we report payments to have per-HTLC granularity.

This may also have some implementation implications (I'm not sure how much information each surfaces). Researching what is available to us is part of the scope of this issue.