[AWS Fargate] Add Memory Hard Limit from container metadata

[lucian-ioan]

Currently, not all metadata from the containers is being parsed by the metricbeat awsfargate module:

beats/x-pack/metricbeat/module/awsfargate/task_stats/container.go

Lines 12 to 18 in 17d5bb1

	// container is a struct representation of a container
	type container struct {
	DockerId string
	Name string
	Image string
	Labels map[string]string
	}

The following line should be added to extract the Hard Limit that will be used in the integration dashboard:

Limits map[string]string

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)