Add read-only support for EmbeddedRocksDB

Why it matters

This feature enables users to access data stored in EmbeddedRocksDB in a read-only mode, allowing for safe querying without the risk of modifying the underlying RocksDB data. It enhances the ability to integrate RocksDB storage with ClickHouse for analytical or reporting use cases where data immutability is important.

How to use it

Users can enable read-only access by configuring the EmbeddedRocksDB table or engine in read-only mode within their ClickHouse setup. This allows queries to retrieve data from RocksDB without performing any write operations.