Simplified query section for alert rule creation

Introduces a simplified version of the query and alert conditions step for creating Grafana-managed alert rules. The default options streamline rule creation with a cleaner header and a single query and condition. For more complex rules, switch to advanced options to add multiple queries and expressions.

This feature is rolling out to Grafana Cloud over the next couple of weeks.

Grafana Enterprise and OSS:

To use this feature, enable the alertingQueryAndExpressionsStepMode feature toggle.