Add more options to pass configuration values

[vflaux]

Feature request:

Currently the components are configured by a single config file. I would like to be able to configure them via additional files or environment variables. When deployed on a kubernetes cluster with the helm chart you currently need to set all the configurations (db hostname, passwords etc.) at install (or template) which is impracticable if you do not know theses values at that time. Adding other ways to set theses variables would allow to get them from other configmaps or secrets which could be set afterward/asynchronously.

Use case:

We deploy all our manifests via flux and use AWS ACK controllers to provision the database with a custom resource. We do not know the database hostname until the database is created and it is then impossible the properly set the values for helm. Moreover the database and redis secrets are stored in Secrets (managed by External Secrets) and again, cannot be passed to helm.