Make ALTER materialized_view MODIFY QUERY Non-Experimental and Deprecate allow_experimental_alter_materialized_view_structure Setting

Why it matters

This change stabilizes the ability to modify the query of materialized views, removing the need for an experimental setting and improving usability and reliability when altering materialized views in ClickHouse.

How to use it

Users can now use the ALTER MATERIALIZED VIEW MODIFY QUERY command directly without enabling any experimental settings. The previous allow_experimental_alter_materialized_view_structure setting is deprecated and should no longer be used.