Container Registry: Change database.enabled type from bool to string

Summary

Update the GitLab Helm chart's Container Registry configuration to support the new string-based database.enabled field as outlined in Epic &19638.

Background

The Container Registry is changing database.enabled from a boolean to a string type that accepts "true", "false", and "prefer" values. The Helm chart needs to be updated to handle this new configuration format.

Implementation

Update the Container Registry configuration in the Helm chart to:

• Support string values for database.enabled: "true", "false", "prefer"
• Maintain backward compatibility with existing boolean configurations
• Update chart templates to generate proper string values in registry configuration
• Update validation logic that handles this field

Success Criteria

• Chart accepts string values for registry.database.enabled
• Backward compatibility maintained for existing boolean configurations
• Chart templates generate proper string values in registry configuration
• Documentation updated to show new string format options

This change prepares the Helm chart for the future "prefer mode" functionality while maintaining compatibility with current deployments.