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Add cop to discourage use of `:always` data consistency

Sylvester Chin requested to merge sc1-prefer-sticky-over-always into master

What does this MR do and why?

This MR updates the SidekiqLoadBalancing/WorkerDataConsistency cop to remind and discourage the use of data_consistency :always unless the worker requires it. The scalability group is advocating for :sticky data consistency as the default moving forward. It is possible that workers are added with :always consistency without much giving it much consideration since it is the default behaviour in the load balancing middleware.

The MR is generated with a rubocop --auto-correct --disable-uncorrectable statement which marks all existing use of :always with a rubocop:todo with https://docs.gitlab.com/ee/development/rake_tasks.html#generate-initial-rubocop-todo-list. There are two ways to proceed:

  1. If the worker indeed requires primary db connection (e.g. write heavy), remove the file from the todo and add a disable
  2. If the worker can be optimised, perform a migrate to :delayed or :sticky via the use of a feature flag and remove it from the todo file.

See gitlab-com/gl-infra/scalability#1811 (comment 1333136504)

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Edited by Sylvester Chin

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