Do not abort server startup for unset mark_cache_size configuration option

Why it matters

Previously, the ClickHouse server would fail to start if the mark_cache_size setting was missing from the configuration. This feature improves usability by allowing the server to start with a default or unset mark_cache_size, preventing unnecessary startup failures and simplifying configuration management.

How to use it

Users do not need to explicitly set the mark_cache_size configuration option to start the server. The server will start normally even if this option is absent from the configuration file.