Added metadata_keep_free_space_bytes setting for metadata storage disk

Why it matters

This setting helps prevent the metadata storage disk from filling up completely by keeping a configurable amount of free space. It ensures more stable operation and avoids potential errors or failures related to disk space exhaustion for metadata storage.

How to use it

Users can enable this feature by setting the metadata_keep_free_space_bytes parameter to the desired number of bytes to keep free on the metadata storage disk in the ClickHouse configuration or at runtime.