Add system.database_engines table and enable independent registration of database engines and interpreters

Why it matters

This feature improves the extensibility and maintainability of ClickHouse by enabling database engines and query interpreters to be registered independently. This modular approach simplifies adding new engines and interpreters without tightly coupling them to the core code, facilitating easier development and customization.

How to use it

Users can query the new system.database_engines table to view available database engines. Developers can register new database engines and interpreters independently in the codebase following the updated modular registration mechanism.