v.20.8Improvement

Create system database with Atomic engine as default

Create system database with Atomic engine by default (a preparation to enable Atomic database engine by default everywhere). #13680 (tavplubix).
Create the system database with the Atomic engine by default.

Why it matters

This change prepares for enabling the Atomic database engine as the default across ClickHouse, improving consistency and reliability by leveraging the Atomic engine's transactional capabilities for system-level data.

How to use it

No explicit action is required from users. The system database will now be created automatically with the Atomic engine. This serves as a groundwork step towards making the Atomic engine the default everywhere in ClickHouse.