feat(faucet): limit number of transfers per batch (#2434)

This PR introduces a configurable batch_size parameter to limit the
number of transfers per batch. The batch_size can be set via
command-line arguments.

Changes made:
- Added a new `batch_size` parameter to `AppArgs` to allow configuration
through command-line.
- If no value is provided for `batch_size`, it defaults to 6000.