Expose params for big5 track

[wangch079]

While testing the rally track, we found that the param number_of_shards and number_of_replicas are not exposed:

2025-05-27 05:34:52,528 ActorAddr-(T|:46129)/PID:37075 esrally.track.loader CRITICAL Some of your track parameter(s) "number_of_replicas" are not used by this track; perhaps you intend to use  instead.

All track parameters you provided are:
- bulk_indexing_clients
- iterations
- number_of_replicas

All parameters exposed by this track:
- bulk_indexing_clients
- bulk_size
- ingest_percentage
- iterations
- target_opensearch
- target_throughput
- warmup_iterations

This PR tries to expose these 2 parameters.

[gareth-ellis]

LGTM