performance: add performance metric: messaging rate

4 nodes, 28 worker threads (4 * 7), 2800 actors (28 * 100)
Total sent message count: 28000000 (2800 * 10000) in 49079818980 nanoseconds (49.079819 s)
Messaging rate: 570499.251666 messages / second

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>