API: messaging service, Add getter for the pending and completed server
API: messaging service, Add getter for the pending and completed server

This patch adds getter for the messeging service server pending and sent
messages.

Signed-off-by: Amnon Heiman <ed5fc74c4692051ad0b19749fd7cea6ec2d74b9e@scylladb.com>

raphaelsc/scylla,kjniemi/scylla,kjniemi/scylla,duarten/scylla,kjniemi/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,duarten/scylla,raphaelsc/scylla,scylladb/scylla,duarten/scylla,raphaelsc/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla