[Backend] Set audit event destination settings for S3 for a Group

Proposal

To facilitate the sending of audit events to an S3 destination, a namespace-owner needs to be able to set the correct configuration.

Implementation Plan

• Create a new database table named audit_events_amazon_s3_configurations and its model AuditEvents::AmazonS3Configuration belonging to a namespace with the schema:

Column Name	Type
namespace_id	bigint
name	text
access_key_id	string
secret_access_key	string
aws_region	string
bucket_name	string

• Create uniqueness scoped to namespace_id, region and bucket_name.