Export RELEASE_NODE for ECS

[jyeshe]

Description

ECS also provides a service discovery via DNS. By using Cluster.Strategy.Kubernetes.DNS, Lightning instances are able to join Erlang cluster (via vendor-free DNS query) to enable the PubSub. It relies on a env var set by AWS themselves (AWS_EXECUTION_ENV).

Refs "AWS Lagos dependency for Lightning clustering."

Validation Steps

1. Set K8S_HEADLESS_SERVICE with the ECS service discovery DNS name
2. Run a task

Additional notes for the reviewer

• Please notice ECS Tasks don't have user data to initialize this variable and the task IP is different from the container instance.
• There is a similar PR on Thunderbolt: https://github.com/OpenFn/thunderbolt/pull/381

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