Add script to release the SDK along the OpenAPI spec

[giograno]

So far, we have manually released the Python SDK, generating the code from the latest OpenAPI spec.
This PR introduces a workflow to automate this process.

Given a LS version in input, we:

• fetch the corresponding OpenAPI spec from the release artifacts in https://github.com/localstack/openapi;
• update the generated code (i.e., generating code from the fetched spec);
• pull the right LocalStack version and run the SDK test suite;
• create and tag a release commit;
• build and push to PyPi
• create a draft release of the SDK;
• create and push a dev version.

The workflow can be manually triggered on an arbitrary version of LS.
To properly integrate this into the release of LS, we can introduce a workflow triggered when a new OpenAPI spec is released that triggers this via repository_dispatch.

[alexrashed]

Awesome! Really nice push towards further streamlining the release pipeline on LocalStack releases! 💯
I only added a bunch of nitpicks, nothing critical, so from my perspective this can be merged as is, or we can tackle these nitpicks right away ;)

[alexrashed]

nitpick (non-blocking): ‏Maybe it would be good to have all the "spec url fiddling" in the script itself? I think it would be nicer / easier to use if the script just takes an optional version argument and in the script it either uses the latest spec or constructs the URL based on the version. What do you think?

[giograno]

Thanks for the suggestion 👍 definitely cleaner, and we could also drop 2 steps from the workflow. Done in 892bf4d

[alexrashed]

nitpick (non-blocking): ‏That's an interesting condition, could you maybe add a comment here to explain what's going on in this line?

[alexrashed]

nitpick (non-blocking): The installation of the right version of localstack is just defined here in the pipeline. But it seems there is also a requirements-spec.txt (which defines localstack as a dependency, but might not be used at all anymore?). I think it would be nice to:

• Clean up / remove the requirements file
• Either extend the readme explaining that one needs to start the right version of LocalStack manually, or integrate an automatic startup of the right version of LocalStack into the pytest conftest / setup.

[giograno]

Good catch. The requirement file is just a leftover from previous iterations.