[FR]: easy integration tests with localstack

I should be able to manually run a test like so:

```
% bazel run //infrastructure/tools/aws:localstack
% docker run --rm -it -p 4566:4566 -p 4510-4559:4510-4559 localstack:bazel
% pytest
```
to execute a test that expects to talk to AWS APIs, without any network connection.

We may also give guidance about using the Testcontainers library to make the test fixture bring up the containers when the test starts.