Added list of env variables for fn-plugins

KRM-functions should be able get env variables.
Reflecting in `build` cmd args added in [1]
for `fn run` cmd.

[1]
https://github.com/kubernetes-sigs/kustomize/pull/2988/

api/internal/plugins/fnplugin/fnplugin.go

@@ -78,6 +78,7 @@ func NewFnPlugin(o *types.FnPluginLoadingOptions) *FnPlugin {
 			EnableStarlark: o.EnableStar,
 			EnableExec:     o.EnableExec,
 			StorageMounts:  toStorageMounts(o.Mounts),
+			Env:            o.Env,
 		},
 	}
 }