Add detailed reasons

[palkan]

What is the purpose of this pull request?

Add ability to provide additional information to failure reasons.

What changes did you make? (overview)

Add details Hash to specify per-rule meta information:

class ApplicantPolicy < ApplicationPolicy
  def show?
    allowed_to?(:show?, object.stage)
  end
end

class StagePolicy < ApplicationPolicy
  def show?
    # Add stage title to the failure reason (if any)
    # (could be used by client to show more descriptive message)
    details[:title] = record.title
     # then perform the checks
    user.stages.where(id: record.id).exists?
  end
end

# when accessing the reasons
p ex.result.reasons.details #=> { stage: [{show?: {title: "Onboarding"}] }

The main purpose of this feature is to generate more descriptive failure messages with i18n.

No breaking public API changes.

PR checklist:

• Tests included
• Documentation updated
• Changelog entry added