Use environment variables in the path of external helm repos

### Expected behavior
I would like to use environment variables in the path of external helm repos, so I can add the authorization there without commiting the credentials.

### Actual behavior
There is an error:
```
Helm release um not installed. Installing...
Error: INSTALLATION FAILED: invalid chart URL format: https://{{.USERNAME}}:{{.PASSWORD}}@helm.example.com/repository/helm/
```

### Information

- Skaffold version: v1.34.0
- Operating system: Windows 10
- Installed via: Chocolatey
- Contents of skaffold.yaml:

```yaml
apiVersion: skaffold/v2beta25
kind: Config
deploy:
helm:
releases:
- name: example
namespace: example
createNamespace: true
repo: "https://{{.USERNAME}}:{{.PASSWORD}}@helm.example.com/repository/helm/"
remoteChart: foo
```
```

### Steps to reproduce the behavior

1. Use the skaffold.yaml
2. `skaffold dev`