fargate: add ability to register both SRV and A records

I have a fargate service.
* Its internal IP should be discoverable via A records to other ec2 instances, for low latency. Tools like curl and .net core libraries don't even support SRV records, so moving exclusively to SRV is painful.
* But it also seems to need a SRV record for HTTP API (api gateway) to create a private integration with 'vpc link'. This is for our "Slack" integration, which needs a public URL. API GW demands a SRV record, not A. (even though it uses the Discover API, not DNS!)

It's frustrating that both record types aren't supported.

Alternatively, if api gw could just use A records...that would work for us.

No repository files or tests are named. Start by reviewing the Fargate service-discovery and API Gateway private-integration requirements described here; done means the service supports the requested A and SRV record use cases for EC2 discovery and VPC Link integration.

Written by the indexing model from the issue text.