Resource schema: TypeList as element for TypeMap

Hello!

I’m creating a provider where one of resource configurations is a map of string slices map[string][]string. Proposed config will look smth like this:

headers = {
  Content-Type = ["text/html", "charset=utf-8"]
}

Schema that I wanted to use:

"headers": {
				Type:     schema.TypeMap,
				Optional: true,
				Elem: &schema.Schema{
					Type: schema.TypeList,
					Elem: &schema.Schema{Type: schema.TypeString},
				},
			}

But I see that TypeList is not supported as TypeMap element.
Currently I work around this by using TypeString and then splitting it by ; to create config value.

What would be a better way to manage this? Should I stick to my workaround or maybe I should file an issue for sdk and try adding support for map of lists?