Lean on CDK for Lambda Layer packaging

At time of writing, the library manually builds layers via calls to the subprocess:

https://github.com/edkeeble/ingest-framework/blob/5d7c636640778fbe2d19173ad49bf5f3bc1e22f6/ingest/stack/pipeline_stack.py#L94-L122

My understanding is this is slightly undesirable because the environment on which you package the layer (ie you're computer) may not match the Lambda runtime environment. As such, CDK includes tooling to build Layers inside of a Docker image matching the Lambda runtime. https://docs.aws.amazon.com/cdk/api/v2/docs/aws-lambda-python-alpha-readme.html#python-layer