[Parquet] Support querying sharded parquet files

[yeya24]

Is your feature request related to a problem? Please describe.
The underlying parquet library we are using supports sharded parquet files recently. Instead of a single TSDB block converted to a single parquet file, now it supports converting 1 TSDB block to multiple sharded parquet files for better conversion performance.

Today, existing parquet reader only supports 1 shard and we hardcoded it. In order to support querying sharded parquet files, we need to avoid hardcoding the shard and try to read the block total shard size somewhere.

Reference:

• https://github.com/cortexproject/cortex/blob/master/pkg/querier/parquet_queryable.go#L237
• https://github.com/cortexproject/cortex/blob/master/pkg/storegateway/parquet_bucket_stores.go#L273

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