Support auto-insert quorum for majority number

Why it matters

This feature allows users to set the insert_quorum setting to 'auto', which automatically calculates and uses the majority number of replicas in a replicated table for quorum inserts. It simplifies the configuration and improves reliability without requiring manual quorum size specification.

How to use it

To enable this feature, set the insert_quorum setting to 'auto' in your INSERT query or in your session settings, for example:

SET insert_quorum = 'auto';
INSERT INTO replicated_table VALUES (...);