Use caching for policies and client objects

[CGarces]

LambdaGuard can be too slow on projects with a lot of Lambda functions.

This PR cache the role policies and the boto3 client objects.

[adeptex]

Hey @CGarces, thanks for your contribution!

It looks good, but could you please provide instructions on how to test this change, what was modified, and why? Docs about AWS caching, some data on how much it has improved speed for you, and in what context.

Looking forward to your feedback!