[terraform] Add S3 bucket name suffix

Summary:

This stack resolves issues encountered when setting up fresh staging AWS account with Terraform.

Unfortunately, S3 bucket names are globally unique, so we can't have a separate bucket named commapp-blob in staging account.
This diff adds a configurable suffix to the bucket names and configures the suffix for staging environment only.

Details in ENG-4573.

Depends on D8713.

Test Plan: Terraform plan on all: dev, staging, prod. No changes on dev and prod.

Reviewers: jon, varun

Reviewed By: jon

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8714