Add support for environment variable placeholders in hot-reloading paths

[dfangl]

Motivation

When specifying a path for hot-reloading, we require an absolute path on the host, as it is expected for docker bind mounts.
However, this has an important limitation: Templates with a path defined or Cloudpods cannot be easily shared between systems where the code location differs.

For example, a checked out repository with the code at /home/user1/shared-repository/src could be checked out at /home/user2/repositories/shared-repository/src at another users machine.

To enable sharing of templates and cloudpods with hot-reloading paths between different machines without modification, this PR will add the option to use environment variables expansion within the hot-reloading paths. A hot-reloading path like $HOST_DIR/src can now be used in the templates or cloud pods, if an environment variable is set in each LocalStack instance using that path, with the concrete absolute path part as its value.

This variable could be defined relative to the docker compose project, for example, using a template like this:

version: "3.8"

services:
  localstack:
    container_name: "${LOCALSTACK_DOCKER_NAME:-localstack-main}"
    image: localstack/localstack
    ports:
      - "127.0.0.1:4566:4566"            # LocalStack Gateway
      - "127.0.0.1:4510-4559:4510-4559"  # external services port range
    environment:
      # LocalStack configuration: https://docs.localstack.cloud/references/configuration/
      - DEBUG=${DEBUG:-0}
      - HOST_DIR=${PWD}
    volumes:
      - "${LOCALSTACK_VOLUME_DIR:-./volume}:/var/lib/localstack"
      - "/var/run/docker.sock:/var/run/docker.sock"

Changes

• The S3Key for a hot-reloading path now accepts placeholders for environment variables using $KEY or ${KEY}

[github-actions]

LocalStack Community integration with Pro

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2 983 tests 2 677 ✅ 306 💤 0 ❌
2 985 runs  2 677 ✅ 308 💤 0 ❌

Results for commit 141ea8a.

♻️ This comment has been updated with latest results.

[joe4dev]

Great flexible idea giving full control to the user @dfangl 💡

Can we add an example to the Hot Reloading docs?

This solution enables a workaround for the CloudPod/Persistence bug #9974
@giograno Do you think this solution is sufficient to resolve #9974?

[giograno]

This solution enables a workaround for the CloudPod/Persistence bug #9974 @giograno Do you think this solution is sufficient to resolve #9974?

That's a great solution 💯 To me, it solves #9974. I am updating the docs!

[joe4dev]

This solution enables a workaround for the CloudPod/Persistence bug #9974 @giograno Do you think this solution is sufficient to resolve #9974?

That's a great solution 💯 To me, it solves #9974. I am updating the docs!

Great, thank you @giograno. Can you link to the updated docs and close #9974?