Support MLFlow tracking server ARN in config.yaml

[jmeisele]

Describe the feature you'd like
MLFlow tracking server arn available in config.yaml file schema

How would this feature be used? Please describe.
This would be used like other default settings in the config.yaml

Additional context
Admins could/would set this resulting in a better user experience as end users would not have to look it up, similar for how we set default bucket, vpc id, security groups, kms key etc in the config.yaml