Adds a new cop to flag the usage of pluck without a limit

What does this MR do and why?

Adds a new cop for to check the usage of .pluck.

Matches:

• pluck(:attribute) is used without setting a limit.

Bad:

module Gitlab
  module BackgroundMigration
    class MyClass < ::Gitlab::BackgroundMigration::BatchedMigrationJob
      def all
        Project.where(user_id: User.pluck(:id))
      end
    end
  end
end

Good:

module Gitlab
  module BackgroundMigration
    class MyClass < ::Gitlab::BackgroundMigration::BatchedMigrationJob
      def all(limit)
        Project.where(user_id: User.limit(limit).pluck(:id))
      end
    end
  end
end

How to set up and validate locally

1. Select a file that is not present in the .rubocop_todo/cop/avoid_using_pluck_without_limit.yml, like app/models/packages/package_file.rb
2. Add a method that uses pluck:

def all
  pluck(:id)
end

3. run bundle exec rubocop app/models/packages/package_file.rb
4. The file must be in the offenses report:

Offenses:

app/models/packages/package_file.rb:140:5: C: Cop/AvoidUsingPluckWithoutLimit: Avoid using pluck without defining a limit. Plucking without a limit can cause database performance degradation.
    pluck(:id)
    ^^^^^

1 file inspected, 1 offense detected

5. Update the all method and add a limit:

def all
  limit(100).pluck(:id)
end

6. run bundle exec rubocop app/models/packages/package_file.rb again.
7. No offenses should be raised:

Inspecting 1 file
.

1 file inspected, no offenses detected

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #432828 (closed)