[Services] Allow monit system tool to monitor the critical processes status running in various SONiC containers.

[yozhao101]

• What I did
  I added a new configuration file called monit_container (container at here represent the container
  name) for each container and then copied this config file into the base image under the directory
  /etc/monit/config.d. In the host, monit will detect the status of all critical processes running in
  various docker containers. Specifically, monit will detect whether a process is in the dead or live
  state. If a process which is monitored went into the dead state or it failed to start, then monit will
  write an alert into syslog. Currently monit will periodically monitor all the process in the period
  120 seconds. We can set a different value for this period.

• How I did it
  I created this configuration file according to the template config file named monitrc in the host.

• How to verify it
  Before we test this, we should disable the auto-restart feature since if we kill a critical process,
  the corresponding container will restart and then the processes will come up again.
  In the host, we can list the critical processes running in each docker container using
  the command docker top container_id. After that, we deliberately kill a process
  using the command kill -9 proc_id. Then we can review the syslog file and will see an
  alert message showing process_name is not running.

[yxieca]

retest vsimage please

[yxieca]

retest vsimage please