Add a jsonencode to the ECR lifecycle policy

[dragonfleas]

Enhancement: Add a jsonencode to the ECR lifecycle policy

There's a potential in the future that we may want the functionality to extend or set more customized rules for lifecycle policy, while having the default remain the state that it is now.

This would either be passing a json string into a variable, or passing more opinionated variables in that the rules are defined in json with. jsonencode helps this by providing a way for terraform engine to process more data types into json. Otherwise you have to rely on string interpolation.