Add /management endpoint provided via Spring Actuator

The new endpoint provide metrics including information about application
health, environment, configuration, beans, caches and performance via
Spring Actuator. Additional custom endpoints for version info and
statistics are available.

Content type `application/json` may not be set for the `Accept` header
of requests to the management API. Otherwise, only a JSON stub is
returned. `application/vnd.spring-boot.actuator.v2+json` or `*/*` should
be used instead.

To allow monitoring of metrics, a Prometheus endpoint is provided via
Micrometer.

Web API documentation:
https://docs.spring.io/spring-boot/docs/2.1.x/actuator-api/html/