Manage Lambda function zips (and Chrome binaries) separately

[konklone]

Either seek to become a collaborator on https://github.com/dhs-ncats/lambda_functions, or support a similar but separate repository.

Update the build process to support/expect bringing in function zips from another place outside this repository.

(And then go back in git history and rewrite it to remove all the heavy binaries/zips from source history, as a courtesy.)