expose the spring application metrics


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


- enable graceful shutdown
- add spring boot actuator and prometheus registry micrometer
- 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.


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

Target: master
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