Introduce callbacks for tenant change methods

[flavorjones]

to allow applications to extend tenant change behavior.

I'm using this functionality in my current project to cascade a second tenant change in another database, something like this:

module ApplicationRecordWithTenantZoneExtension
  extend ActiveSupport::Concern

  class_methods do
    def with_zone(&block)
      ZonedRecord.with_tenant(tenant_zone, &block)
    end

    def set_queue_zone
      ZonedRecord.current_tenant = tenant_zone
    end

    def tenant_zone
      # ... business logic to determine the "zone" for ApplicationRecord.current_tenant
    end
  end

  included do
    set_callback :with_tenant,        :around, :with_zone
    set_callback :set_current_tenant, :after,  :set_zone
  end
end

Rails.application.config.to_prepare do
  ApplicationRecord.include ApplicationRecordWithTenantZoneExtension
end

so that the application only needs to call ApplicationTenant.with_tenant and the tenant is automatically set on the secondary database as well.