Added trigger for namespace_aggregation_worker

What does this MR do and why?

Adds a trigger for namespace_aggregation_worker when container_registry_size is updated in project_statistics

Ref: https://gitlab.com/gitlab-org/gitlab/-/issues/358389

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How to set up and validate locally

1. Open rails console and get Project from a namespace
2. Update the container_registry_size for the project_statistics of the project
3. Trigger project_statistics.refresh! or ps.refresh!(only: [:container_registry_size])
4. Validate Namespaces::ScheduleAggregationWorker is triggered via sidekiq: gdk redis-cli monitor | grep -i ScheduleAggregationWorker

[1] pry(main)> n = Namespace.where(:path => 'suraj').first
[2] pry(main)> p = n.all_projects.first
[3] pry(main)> ps = p.statistics
[8] pry(main)> ps.refresh!
=> true
[8] pry(main)> ps.refresh!(only: [:container_registry_size])
=> true

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