IAM authentication to access the Database

Summary It would be great if Directus would become capable of authenticating to the database using a Service Account / Service Principal and IAM permissions in a cloud environment instead of requiring the use of plain password. There is currently possible to achieve that but the solution is very hacky. Basic Example Say I want to deploy Directus to Cloud Run. I can configure there an integration with Cloud SQL. Instead of specifying the DB_PASSWORD I would set something like DB_IAM_AUTH=gcp and Directus would configure Knex to use a Google Cloud Access Token for the password and refresh it before expiring. Motivation Moving away form secrets in favor of temporary tokens has become the trend now as it reduces the risk of getting the database compromised if the service is compromised and makes secret management easier. Additionally, it's a step forward in making security easier as handling a database secret can be done wrong, while configuring token based authentica…