expose the spring application metrics

Motivation:

To gain insight on marketplace-app, the spring framework provide
the facility to expose the application metrics to monitoring
service like Prometheus on Kubernetes.

Modification:

- enable graceful shutdown
- add spring boot actuator and prometheus registry micrometer
    dependencies
- expose the actuator endpoint that will provides: health,
   info, metric etc.
- avoid 404 error on request to /favicon.ico
- add a mapping for '/scripts/config.js' and generate the necessary
    configuration parameter for the web-app static file. This enable
    us to configure the cerebrum endpoint.

Results:

This application now makes it metrics available and can be shutdown
gracefully. Also, moved the config javascript into the application.

Target: master
4 jobs for master in 4 minutes and 46 seconds