Add support for browsing event registries in other accounts

[nmoutschen]

Amazon EventBridge Schema Registries support giving read access to other AWS accounts and browsing those by passing the complete ARN.

However, registries in other AWS accounts don't appear with the listRegistries operation, thus will not appear in the evb cli.

One way to support this would be to add a --registry-name option to explicitly specify a registry name or ARN.