Set LOCALSTACK_HOST from service name

[simonrw]

Motivation

LocalStack 3.0.0 standardises LOCALSTACK_HOST for services that return URLs. This configuration variable is substituted for domain names if customised. This means for example, that when creating an SQS queue, rather than receiving a queue URL of something like:

http://sqs.eu-west-1.localhost.localstack.cloud:4566

you receive (with LOCALSTACK_HOST=foo.bar):

http://sqs.eu-west-1.foo.bar:4566

This is important in k8s because the service name is a general DNS entry that resolves to the LocalStack pod. When users of the returned URL try to make calls to that URL, it will now succeed.

Changes

• set the pod LOCALSTACK_HOST environment variable to match the k8s service name

[simonrw]

This could be handled by user configuration, we should not try to automatically infer this value from the environment.