Fix autodiscover for docker in filebeat

[kaiyan-sheng]

Results from autodiscover for docker with filebea have docker.container.id fields instead of the ECS fields container.id. This PR is to figure out why this is happening.

With this change, now in ES, filebeat output looks like:

[kaiyan-sheng]

Now the output contains both container.id and docker.container.id and same for container.image.name, container.name and container.labels. Is this expected? I need to spend more time to figure this out.

[kaiyan-sheng]

Interesting "discover":

1. container.* and docker.container.* are both from docker autodiscover meta field.
2. If comment out "container": metaNew, in docker autodiscover, then the filebeat metrics will only have docker.container.* fields but not container.*.

		event := bus.Event{
			"provider":  d.uuid,
			"id":        container.ID,
			flag:        true,
			"host":      host,
			"docker":    metaOld,
			"container": metaNew,
			"meta": common.MapStr{
				"docker":    metaOld,
				// "container": metaNew,
			},
		}

With this event meta, enable add_docker_metadata processor in filebeat.yml with labels.dedot: true, docker.container.labels are not dedotted.

2. If comment out "docker": metaOld, in docker autodiscover, then the filebeat metrics will only have container.* fields but not docker.container.*.

		event := bus.Event{
			"provider":  d.uuid,
			"id":        container.ID,
			flag:        true,
			"host":      host,
			"docker":    metaOld,
			"container": metaNew,
			"meta": common.MapStr{
				// "docker":    metaOld,
				"container": metaNew,
			},
		}

With this event meta, enable add_docker_metadata processor in filebeat.yml with labels.dedot: true, container.labels are successfully dedotted.

[kaiyan-sheng]

jenkins, test this please

[kaiyan-sheng]

Because this PR is originally started with Nicolas's work. I will close this PR and recreate a new one #10862 based on his PR.