Spring Boot sample with Redis export for metrics.

Start redis, e.g. with [Docker Compose]()

[source,indent=0]
----
	$ docker-compose up
----

Run the app and ping the home page (http://localhost:8080) a few times. Go and look at
the result in Redis, e.g.

[source,indent=0]
----
	$ redis-cli
	127.0.0.1:6379> keys *
	1) "keys.spring.metrics"
	2) "spring.metrics.counter.status.200.root"
	3) "spring.metrics.gauge.response.root"
	127.0.0.1:6379> zrange keys.spring.metrics 0 0 WITHSCORES
	1) "spring.metrics.counter.status.200.root"
	2) "4"
----

There is also an `AggregateMetricReader` with public metrics in the application context,
and you can see the result in the "/metrics" (metrics with names in "aggregate.*").
The way the Redis repository was set up (with a random key in the metric names) makes the
aggregates work across restarts of the same application, or across a scaled up application
running in multiple processes. E.g.

[source,indent=0]
----
	$ curl localhost:8080/metrics
	{
		...
		"aggregate.application.counter.status.200.metrics": 12,
		"aggregate.application.counter.status.200.root": 29,
		"aggregate.application.gauge.response.metrics": 43,
		"aggregate.application.gauge.response.root": 5,
		"counter.status.200.root": 2,
		"counter.status.200.metrics": 1,
		"gauge.response.metrics": 43,
		"gauge.response.root": 5
	}
----

