[packaging] utilize a lambda layer for rules in the rules engine lambda #1271
Description
Background
As we move toward packaging improvements, we should consider using an AWS Lambda Layer for management of rules deployed to the rules engine.
Desired Change
Add support for zipping / applying a new lambda layer for streamalert rules without having to deploy the rule rules engine code.
Things to consider:
Third party dependencies used by rules that are not part of the 'core' rules engine code. Maybe have a secondary layer for these?