feat: configure CI environment to talk to LocalStack

[simonrw]

Motivation

When using the setup-localstack action, the user currently has to set AWS_ENDPOINT_URL to target LocalStack. This is inconvenient - if we are providing a helper action to configure LocalStack then we should set the CI environment as well.

Changes

• Set AWS_ENDPOINT_URL by default to http://localhost.localstack.cloud:4566
• Add option to disable

Thanks @dfangl for the idea!

[github-actions]

The ephemeral instance for the application preview has been shut down

[steffyP]

Thanks a lot for the addition @simonrw 🙏
It would be great if we could add this to the README as well (at least before the next release).
Personally I think this is good to merge :)

I am not sure what the upcoming release strategy is though (I only helped out with a cleanup initiative).

/cc @dominikschubert - could you maybe assign the PR to the new repo owner(s)?

[dominikschubert]

Great idea overall! Looking at potential hybrid scenarios, I'm just not sure we should make this the default, at least for now. Adding it first as an option would also be less of a breaking change (even though we're still on 0.x and not bound by semver).