Log split queries at query frontend

[yeya24]

What this PR does:

This pr adds a single counter to querier_stats to count number of queries sent to grpcRoundTripperAdapter, which is basically the number of split queries or number of queries sent to request queue.

Now it will be logged along with the query stats log.

ts=2023-12-08T19:20:28.345331Z caller=handler.go:364 level=info org_id=fake traceID=b3a337ac639f353f7647018811c908c5 msg="query stats" component=query-frontend method=GET path=/prometheus/api/v1/query response_time=10.184291ms query_wall_time_seconds=0.065051376 fetched_series_count=0 fetched_chunks_count=0 fetched_samples_count=0 fetched_chunks_bytes=0 fetched_data_bytes=0 split_queries=10 status_code=200 response_size=63 shard_by.is_shardable=true shard_by.num_shards=10 shard_by.sharding_labels=[job] query_length=16 user_agent=PostmanRuntime/7.35.0 param_query="sum(up) by (job)"

Which issue(s) this PR fixes:
Fixes #

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]