Use S3's STANDARD_IA Storage Class for Auditing Buckets by default

[eduardohki]

Is your feature request related to a problem? Please describe.
Since the CloudTrail/FlowLogs/S3 Access Logs stored in the main account's auditing S3 buckets usually don't have many, consistent read access, so it makes sense to set STANDARD_IA as a default storage class to save some dollars.

Describe the solution you'd like
All S3 buckets created under main-account-stacks/01-auditing/ should have a variable to set the S3's storage class, defaulting to STANDARD_IA.

Describe alternatives you've considered
I considered also to have the flexibility to set it up per bucket, however I don't see this a common use-case anyway.

Additional context
N/A