Support for custom resources to utilize values.yaml

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

A common pattern for configuring a UI in Kubernetes is to create an `app-config.json` and inject it into the container at some pre-defined directory. The UI then reads in this config file and uses it to... configure itself. I'm sure it's possible to create an extension method using current tools that can do this, but the problem is there is no way to have it parameterized with `values.yaml`.

### Describe the solution you'd like

First-class Aspire resources have the ability to add entries into a helm chart's values.yaml file. A common example of this would be `.WithEnvironment`, which both adds an entry to values.yaml, and references the placeholder in the config-map file. It would be nice if this functionality was exposed in a way that allowed custom/third-party resources to do the same.

### Additional context

_No response_