[Runner Fleet dashboard] API for percentiles of job wait time for runners over 3 hours

1. Add database schema based on POC for ci analytics on ClickHouse (!126863 - closed)
2. Add GraphQL API based on this schema to support view in Visualize percentiles of estimated job wait tim... (#411966 - closed)
3. API should be in alpha version and should be behind the feature flag
4. API should only be available to admins.