Adds a cop for rescued exceptions in BBM job classes

What does this MR do and why?

Adds a new cop for Batched Background Migration Jobs.

Matches:

• If is a sub-class of: Gitlab::BackgroundMigration::BatchedMigrationJob or BatchedMigrationJob
• If rescue statements inside methods: rescue => e, rescue StandardError => e, JSON::ParserError, ActiveRecord::StatementTimeout => error

Bad:

module Gitlab
  module BackgroundMigration
    class MyClass < ::Gitlab::BackgroundMigration::BatchedMigrationJob
      def perform
        execute
      rescue => error
        logger.error(message: error.message, class: self.class.name)
      end
    end
  end
end

Bad:

module Gitlab
  module BackgroundMigration
    class MyClass < ::Gitlab::BackgroundMigration::BatchedMigrationJob
      def perform
        execute
      rescue StandardError => error
        logger.error(message: error.message, class: self.class.name)
      end
    end
  end
end

Good:

module Gitlab
  module BackgroundMigration
    class MyClass < ::Gitlab::BackgroundMigration::BatchedMigrationJob
      def perform
        execute
      rescue StandardError => error
        logger.error(message: error.message, class: self.class.name)
       
        raise
      end
    end
  end
end

Example: https://gitlab.com/gitlab-org/gitlab/-/jobs/4473111652

How to set up and validate locally

1. Go to lib/gitlab/background_migration/set_correct_vulnerability_state.rb - or any other batch background migration job class
2. Update the perform method to:

def perform
  each_sub_batch do |sub_batch|
    sub_batch.update_all(state: DISMISSED_STATE)
  rescue StandardError => error
    puts error
  end
end

3. run bundle exec rubocop lib/gitlab/background_migration
4. The file must be in the offenses report

Inspecting 151 files
................................................................................................................................................C......

Offenses:

lib/gitlab/background_migration/set_correct_vulnerability_state.rb:16:9: C: BackgroundMigration/AvoidSilentRescueExceptions: Avoid rescuing exceptions inside job classes. Jobs can be erroneously marked as successful, even when they fail. Consider re-raising the error if rescuing this exception is needed.
        rescue StandardError => error
        ^^^^^^^^^^^^^^^^^^^^

151 files inspected, 1 offense detected

5. Update the perform again. Add the raise statement:

def perform
  each_sub_batch do |sub_batch|
    sub_batch.update_all(state: DISMISSED_STATE)
  rescue StandardError => error
    puts error

    raise
  end
end

6. run bundle exec rubocop lib/gitlab/background_migration again.
7. The file must be left out of the offenses report

Inspecting 151 files
.......................................................................................................................................................

151 files 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 #403073 (closed)