Create ClickHouse ai_usage_events_daily table

What does this MR do and why?

Create ai_usage_events_daily table on CH to aggregate event ocurrences per day.

This will be used to support the GraphQL field to be introduced with #570987.

How to set up and validate locally

bundle exec rake gitlab:clickhouse:migrate

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.