Feature: Support mounting an S3 bucket under SharedStorage

It seems that mounting an S3 bucket on parallelcluster is already possible through postinstall tasks: https://github.com/aws-samples/aws-hpc-s3mountpoint. Same may be possible for [S3 Files](https://aws.amazon.com/s3/features/files/).
Is possible or planned to enable _s3mountpoint_ and or _S3 Files_ via `SharedStorage` https://docs.aws.amazon.com/parallelcluster/latest/ug/SharedStorage-v3.html such that one can chose to enable readonly access?

Start with the SharedStorage v3 documentation and the linked aws-hpc-s3mountpoint postinstall-task example. Compare the proposed s3mountpoint and S3 Files approaches, including readonly access, and define what configuration would enable each under SharedStorage.

Written by the indexing model from the issue text.