The dynamic-from-file:// syntax is supported for metadata database URLs but not for data source database URLs

### Issue description

The dynamic-from-file:// syntax is supported for metadata database URLs but not for data source database URLs in Hasura's current implementation.

Observed per doc: https://hasura.io/docs/2.0/security/dynamic-secrets/#configuration-for-metadata-database

### Describe the solution you'd like

Allow users to set `DATABASE_URL` from_env' variables in _metadata/databases.yaml_ file with the ability to be set to _dynamic-from-file_ for data source database urls, like the graphql metadata env url.

### Workaround

When a sed command (a stream editor tool in Unix/Linux) to edit the databases.yaml file during deployment.

This command replaces instances of from_env with dynamic-from-file specifically for staging.