Merge Tables Enhancements and Compatibility Considerations

Merge tables will unify the structure of underlying tables by using a union of their columns and deriving common types. This closes #64864. In certain cases, this change could be backward incompatible. One example is when there is no common type between tables, but conversion to the type of the first table is still possible, such as in the case of UInt64 and Int64 or any numeric type and String. If you want to return to the old behavior, set merge_table_max_tables_to_look_for_schema_inference to 1 or set compatibility to 24.12 or earlier. #73956 (Alexey Milovidov).