Consider `RouteParameters::max_total_routing_fee_msat` in `get_route`

Consider `RouteParameters::max_total_routing_fee_msat` in `get_route`

We exclude any candidate hops if we find that using them would let the
aggregated path routing fees exceed `max_total_routing_fee_msat`.

Moreover, we return an error if the aggregated fees over all paths of
the selected route would surpass `max_total_routing_fee_msat`.