fix: "cannot unmarshal !!str <no value> into bool" errors in state templates (#645)

Seems like we are affected by https://github.com/golang/go/issues/24963. That is, even though we internally use the template option `missingkey=zero`, in some cases it still prints `<no value>` instead of zero values, which has been confusing the state yaml parsing.

This fixes the issue by naively replacing all the remaining occurrences of `<no value>` in the rendered text, while printing debug logs to ease debugging in the future when there is unexpected side-effects introduced by this native method.

Fixes #553

pkg/tmpl/context_tmpl.go

@@ -13,9 +13,9 @@ func (c *Context) stringTemplate() *template.Template {
 	}
 	tmpl := template.New("stringTemplate").Funcs(funcMap)
 	if c.preRender {
-		tmpl.Option("missingkey=zero")
+		tmpl = tmpl.Option("missingkey=zero")
 	} else {
-		tmpl.Option("missingkey=error")
+		tmpl = tmpl.Option("missingkey=error")
 	}
 	return tmpl
 }