Add database validations for audit_events_amazon_s3_configurations

Description

We recently got a sentry alert [INTERNAL URL] that 'bucket name must not contain a forward-slash'. This error was raised while streaming an even to AWS S3. These do not contribute to the error budget since we safely rescue these errors here but we should still fix them so that users are unable to create rows with invalid bucket names or other params.

Proposal

Add database and model validations for all such cases following the Amazon S3 docs.