LocalStack CLI doesn't respect version

[chrisbloe]

Overview

When running the following GitHub Action...

      - name: Start LocalStack
        uses: LocalStack/setup-localstack@v0.3.0
        with:
          install-awslocal: "true"
          use-pro: false
          image-tag: "4.14.0"

...the pro version is not used, however, the code which installs the CLI defaults to the latest CLI version (and not the image-tag value provided:

The file tools/action.yml contains the line...

        which localstack > /dev/null || pip install localstack

...which installs the latest version only.

I believe this line should be modified to accept a version override (image-tag) if one is provided. This may also be the cause of #24.