Allow to Use Clickhouse-copier with Cross-replication Cluster Topology by Permitting Empty Database Name

Why it matters

This enhancement enables clickhouse-copier to work seamlessly in complex cross-replication environments where specifying a database name is not always required or possible. It simplifies data copying operations across clusters with cross-replication setups, improving flexibility and usability.

How to use it

When configuring clickhouse-copier for a cross-replication cluster, set the database name parameter to be empty or omit it. This permits clickhouse-copier to function correctly without explicitly requiring a database name in the configuration files.