Feature Request: HTTP Resolver to Private ELB or VPC Link support

We're looking to invoke an AppSync HTTP resolver to an internal NLB. Currently, we do this with a VPC Link in API Gateway. We could tie the HTTP Resolver to the API Gateway, but that seems like overkill.

Are there plans to support internal endpoints?
- Lambdas inside a VPC
- Internal ELB(s)

I tried following the invoking AWS Services in the HTTP Resolver tutorial, but had no luck.
https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-http-resolvers.html

Start with the linked AWS HTTP resolver tutorial and the issue discussion about VPC Link, internal NLB/ELB endpoints, and VPC Lambdas. The request is complete only when support for internal endpoints is established and the supported approach is documented or implemented.

Written by the indexing model from the issue text.