Multi AWS Account guidance

I'm sure we're not the only one running multiple AWS Accounts but a single Consul cluster across all accounts, with service names indicating aws account (dev, test, etc).

Since cloud map seems to be a per-account service, it would be good to have some guidance on how to set up consul-aws against multiple accounts.

Start by reviewing consul-aws's setup and AWS Cloud Map integration, focusing on the stated case of one Consul cluster spanning multiple AWS accounts. Document the supported configuration and account boundaries for account-specific service names; the issue provides no file or test to target.

Written by the indexing model from the issue text.