Add support for Serverless Framework packages

[volkangurel]

The Serverless Framework allows functions to be packaged into a directory, stored, and deployed in a separate step. This aligns well with CI/CD workflows, including the ones implemented in vili.

vili should support reading a repository of packaged functions (e.g. in S3), with a naming convention similar to docker tags (in a directory structure to mimic tags) and calling the serverless deploy command to deploy a given tag.