Option to fail if any dependency wheels are missing

Currently, missing dependencies are unconditionally translated into advisory warnings:

https://github.com/aws/chalice/blob/1cdebd90d66435c26958687a1d6a3670eeb06293/chalice/deploy/packager.py#L84-L88

This can result in broken deployments if requirements.txt changes and I forget to vendor a wheel that can't be automatically found.

I'd like to have an option to fail the deployment if any dependency wheels are not found.

Start at chalice/deploy/packager.py lines 84-88, where missing dependency wheels are translated into advisory warnings. Trace how dependency packaging options reach deployment and identify the existing tests for this path; done means an option causes deployment to fail whenever any required wheel is missing.

Written by the indexing model from the issue text.