[Backend] Set audit event destination settings for AWS S3 for an instance

Proposal

To facilitate the sending of audit events to an S3 destination, an instance admin needs to be able to set the correct configuration at the instance level settings.

Implementation Plan

• Create a new database table named audit_events_instance_amazon_s3_configurations and its model AuditEvents::Instance::AmazonS3Configuration belonging to a namespace with the schema:

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

• Create uniqueness scoped to region and bucket_name.