Rolling upgrade support for in-flight requests

Rolling upgrade support for in-flight requests

Three entry points are being handled :
 1 - REST endpoint
 2 - gRPC endpoint
 3 - Kafka consumer

We make use of Phaser object to make sure the PreDestroy callback wait
for all requests to be executed before stopping the process.

The docker image was also modified to make sure the java process becomes
PID 1 in the container in order to catch the SIGTERM signal which
triggers the PreDestroy callback of Spring. This was done by using
the "exec" command in bash.

Issue-ID: CCSDK-1885
Signed-off-by: Sebastien Premont-Tendland <sebastien.premont@bell.ca>
Change-Id: I3e2a72e26a4c8b7768ebc374ea40aa8d55fb6761