Add option to utilize Miserlou/lambda-packages

[azatoth]

https://github.com/Miserlou/lambda-packages contains various packages compiled to be used in aws lambda. It would be nice to be able to utilize his package (needing psycopg2). At the moment I have to inject the library from the outside using --extra-files as 1. it contains multiple libraries, and 2. they are as tar ball in the package.

As a general solution, a way to run a script before packaging the zip would be enough