[ECS]: Support "A" Records with ECS Service Discovery when `host` networking is used

**Tell us about your request**
Support "A" Records with ECS Service Discovery when `host` networking is used.

**Which service(s) is this request for?**
ECS/Cloud Map

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
I would like to be able to easily connect to my services from a cli http client or a browser using the domain name provided by by service discovery. SRV records are not supported by most off the shelf tools so I am requesting support for A records.

**Are you currently working around this issue?**
I am registering the services at the host level using user data scripts and de-registering them using instance termination hooks

**Additional context**
I understand that A records at the host level limit the usefulness of service discovery to a single service per instance, but I am fine with that.

No repository files, tests, or entry points are identified. Start by reviewing the ECS/Cloud Map service-discovery behavior for host networking and the distinction between A and SRV records; done means services can be reached through the service-discovery domain by a CLI HTTP client or browser, while accounting for the one-service-per-instance constraint.

Written by the indexing model from the issue text.