Move Shimo integration to the JiHu codebase

Description

Move Shimo integration to the JiHu codebase.

15.7

• Add deprecation entry !106183 (merged)

16.6 (see thread)

• Remove code
• Add removal entry
• Remove usage ping metric
• Remove documentation https://docs.gitlab.com/ee/user/project/integrations/shimo.html
• Delete database records

  Integration.each_batch(of: 1000, column: :id) do |relation|
    relation.delete_by(type_new: 'Integrations::Shimo')
  end

16.7

• Remove leftover code, dummy model
• Remove IntegrationShimo issues, merge requests, epics and label

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For reference about how to remove an integration #379197 (closed).