Create LambdaSupervisor process module

[igaray]

Create a LambdaSupervisor module, which is actually a GenServer behaviour, which will run the lambdas in a separate process by calling the user-provided callbacks from the GenLambda module, and will monitor them and kill in they timeout.

This module will gather the metrics for lambda executions and limit the running time to a configurable value.

This module is part of the lambda_core application