Add configurable limit for query batching

[lennyburdette]

Describe the solution you'd like

Support a limit on the number of requests in a batch, effectively enforcing the client-side setting. For example:

batching:
  enabled: true
  mode: batch_http_link
  max_requests: 10

Describe alternatives you've considered

AFAIK it's not possible to use Rhai/coprocessors to enforce this because the parsed batch body is not available within extensions points.

Additional context

Raised on behalf of a customer