Make it possible to obtain a reference of type Container to services started by Docker Compose

[bsideup]

Since DockerComposeContainer#project is private, there is currently no way of accessing containers started by Docker Compose.

We should add a public API to access them, something like:

public ContainerState getServiceContainer(String serviceId);

We already do something similar here:

testcontainers-java/core/src/main/java/org/testcontainers/containers/DockerComposeContainer.java

Lines 256 to 263 in 500fd74

	private List<Container> listChildContainers() {
	return dockerClient.listContainersCmd()
	.withShowAll(true)
	.exec().stream()
	.filter(container -> Arrays.stream(container.getNames()).anyMatch(name ->
	name.startsWith("/" + project)))
	.collect(toList());
	}

And store it in:

testcontainers-java/core/src/main/java/org/testcontainers/containers/DockerComposeContainer.java

Line 71 in 500fd74

private final Map<String, ComposeServiceWaitStrategyTarget> serviceInstanceMap = new ConcurrentHashMap<>();

Which means that the implementation should be a simple look up.

This will also solve #1916 and similar requests.

[artjomka]

I would like to work on this issue, if its not taken already