feat: specify env values from the parent to the nested state (#622)

* feat: specify env values from the parent to the nested state

Adds the `helmfiles[].environment.values` that accepts a mix of file pathes and inline dictes:

```yaml
helmfiles:
- path: path/to/nested/helmfile.yaml
  environment:
    values:
    - key1: val1
    - values.yaml
```

The values files are loaded in the context of the parent state file. For example, in case the above state file is located at `/path/to/helmfile.yaml`,
`values.yaml` is located at `/path/to/values.yaml` instead of `/path/to/nested/values.yaml`.

Resolves #523

* fix: multiple "bases" declarations yields duplicate releases

Fixes #615

* fix regression in double-rendering with env value overrides

The latest commit broke any state files like the below to NOT pass env value overrides at all:

```
helmfiles:
- path: nested/state.yaml
  environment:
    values:
    - overrides.yaml
```

This fixes the issue.

cmd/cmd.go

@@ -25,7 +25,7 @@ func VisitAllDesiredStates(c *cli.Context, converge func(*state.HelmState, helme
 		return converge(st, helm, ctx)
 	}
 
-	err = a.VisitDesiredStates(fileOrDir, a.Selectors, convergeWithHelmBinary)
+	err = a.VisitDesiredStates(fileOrDir, app.LoadOpts{Selectors: a.Selectors}, convergeWithHelmBinary)
 
 	return toCliError(c, err)
 }