FAB-13067 Add blockcutter metrics

The only real tunables for the orderer as far as latency and throughput
goes is the batch parameters.  Therefore, it's critical for network
operators to be able to gain insight into the duration filling a block
takes to know whether they should relax or tighten their batch
parameters.

Change-Id: I9f64116f16b3138c1bb1cce11b00787f630a7141
Signed-off-by: Jason Yellick <jyellick@us.ibm.com>