Add cop to restrict Sidekiq.redis and Gitlab::Redis::Queues

Description of the proposal

This MR restricts the use of general usage Sidekiq.redis in application. The permitted use-cases are for migration and admin operations. Interactions with sidekiq should be done through Sidekiq APIs (migration/admin only) or .perform_{async/in} or bulk variants in non-migration/admin logic rather than directly sending commands to redis.

See gitlab-com/gl-infra/scalability#1939

New cop rule: Refrain from directly using Sidekiq.redis unless for migration and admin operations.

Check-list

• Make sure this MR enables a static analysis check rule for new usage but ignores current offenses.
• Mention this proposal in the relevant Slack channels (e.g. #development, #backend, #frontend).
• If there is a choice to make between two potential styles, set up an emoji vote in the MR:
  • CHOICE_A: 🅰
  • CHOICE_B: 🅱
  • Vote for both choices, so they are visible to others.
• The MR doesn't have significant objections, and is getting a majority of 👍 vs 👎 (remember that we don't need to reach a consensus).
• (If applicable) One style is getting a majority of vote (compared to the other choice).
• (If applicable) Update the MR with the chosen style.
• Create a follow-up issue to fix the current offenses as a separate iteration: ISSUE_LINK
• Follow the review process as usual.
• Once approved and merged by a maintainer, mention it again:
  • In the relevant Slack channels (e.g. #development, #backend, #frontend).
  • (Optional depending on the impact of the change) In the Engineering Week in Review.