feature request: Support for multiple values files, and values files outside of "root"

[cNorspang]

It would be great, for a multi-environment setup, if we could somehow give a list of values files to take into consideration, potentially with a heirachy akin to how ArgoCD does it

eg.

apps/
├── app1/
│   ├── Chart.yaml
│   ├── templates/
│   │   └── deployment.yaml
│   └── values/
│       ├── dev.yaml
│       ├── staging.yaml
│       └── prod.yaml
└── app2/
    ├── Chart.yaml
    ├── templates/
    │   └── deployment.yaml
    └── values/
        ├── dev.yaml
        ├── staging.yaml
        └── prod.yaml
configuration/
└── values/
    ├── dev.yaml
    ├── staging.yaml
    └── prod.yaml
    └── generated/
        ├── dev.yaml
        ├── staging.yaml
        └── prod.yaml

If I, for any given chart, could tell it to consider dev.yaml within a set of predefined paths ["../../configuration/values", "../../configration/generated/values", "./values"]

And i would do that as a heirachy, applying first -> last, so the "resulting" value, in case of conflict in all files would be the one in "./values/dev.yaml"