Add support for port mapping in docker hints

[ChrsMark]

What does this PR do?

Add support for port mapping in docker autodiscover. The idea is similar to what we do for Kubernetes which was added at #19398.

The idea is to make it possible for collecting metrics using the HostPort of the container as described at #19825, by referring to the proper internal port of the container (see manual testing notes for an example).

Why is it important?

To cover cases like #19825.

How to test this PR locally

1. Use the following configuration:

metricbeat.autodiscover:
  providers:
    - type: docker
      hints.enabled: true

output.console:
  pretty: true

2. Run metricbet with ./metricbeat -e -d "module" -c metricbeat.yml
3. Start a target container with docker run --name nats --rm -p 4222:4222 -p 8081:8222 --label co.elastic.metrics/module="nats" --label co.elastic.metrics/metricsets="stats" --label co.elastic.metrics/hosts='localhost:${data.ports.8222}' nats:2.1.4 --http_port 8222
4. Verify in the console output that Metricbeat is collecting metrics properly from localhost:8222 endpoint.

Related issues

• Closes Metricbeat: Hint based autodiscover for docker does not work when internal and exposed port differ #19825
• Relates Add support for named ports in autodiscover (hints & templates) #19398

[botelastic]

This pull request doesn't have a Team:<team> label.

[jsoriano]

Nice. LGTM.

Please add a changelog entry.

And would it be possible to add tests for this?

[ChrsMark]

Nice. LGTM.

Please add a changelog entry.

And would it be possible to add tests for this?

Yeap, I'm planning to add docs/changelog and good idea adding tests too!

[elasticmachine]

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• Start Time: 2022-04-12T12:44:02.021+0000

• Duration: 83 min 12 sec

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Total	24234

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[jsoriano]

Nit. Consider defining new method to keep backwards compatibility. Though probably nothing is using this method outside of beats.

Suggested change

	func (c Client) ContainerStart(image string, cmd []string, labels map[string]string, hostConfig *container.HostConfig) (string, error) {
	// ...
	type StartOptions struct {
	HostConfig *container.HostConfig
	}
	// ...
	func ContainerStart(image string, cmd []string, labels map[string]string) (string, error) {
	return ContainerStartWithOptions(image, cmd, labels, StartOptions{})
	}
	// ...
	func (c Client) ContainerStartWithOptions(image string, cmd []string, labels map[string]string, options StartOptions) (string, error) {
	...

[ChrsMark]

Thank you! This test is not correct nevertheless so I will revert this. Unfortunately we don't have proper tests at the moment that I could extend to cover this feature addition.

[MichaelKatsoulis]

LGTM