Implemented Comment Change for ReplicatedMergeTree Tables

Why it matters

This feature allows users to modify the comment metadata of ReplicatedMergeTree tables, enabling better table documentation and clarity without needing to recreate the table or lose replication settings.

How to use it

Users can change the comment on an existing ReplicatedMergeTree table using the standard ALTER TABLE statement with the COMMENT clause. For example:

ALTER TABLE table_name COMMENT 'New comment';