`listSandboxes` should allow `maxItems` argument

[johnpc]

Environment information

N/A

Description

Right now, pagination of listSandboxes in deployed_backend_client.ts does not make any guarantees about the number of items it returns.

See this comment: https://github.com/aws-amplify/amplify-backend/pull/258#discussion_r1340299285

We should improve this api so that the behavior is more ergonomic