Research container usage in IT's and add README.md

[sming]

add the README.md to in /heroic/heroic-test.

Focus on ES container as well to make sure we understand how/where/what we're using.

Are CI and running it locally identical?

See fb4b2d2?w=1 - this PR introduced containers it's thought.

Also see org.testcontainers.containers.GenericContainer usage in /Users/peter/src/spotify/heroic/metric/bigtable/src/test/java/com/spotify/heroic/metric/bigtable/BigtableBackendIT.java

Also see heroic/heroic-dist/src/test/java/com/spotify/heroic/PubSubConsumerIT.java .