Store and update namespace statistics in a performant manner

What this post added

Introduced an asynchronous approach to update namespace storage statistics using Sidekiq jobs and Redis for lease management. This avoids increasing the transaction length of project statistics updates and improves performance for large namespaces. The solution involves creating a `namespace_aggregation_schedules` table, enqueuing Sidekiq jobs for immediate and delayed execution, and using Redis leases to prevent concurrent aggregations. A cron job is also scheduled to process any remaining pending updates.