Rails runner support

[adamyeats]

Add support for error reporting from inside Rails runners: https://guides.rubyonrails.org/command_line.html#rails-runner

[tombruijn]

@xadamy can you link to the intercom convo that brought this to our attention?

[adamyeats]

https://app.intercom.com/a/apps/yzor8gyw/inbox/inbox/conversation/16410700002295

[raulr]

As a workaround I add this inside the Application class in config/application.rb:

runner do
  next unless defined?(Appsignal) && Appsignal.active?

  action_name = ARGV.first&.truncate(50) || "unknown"

  Kernel.at_exit do
    next unless $!

    Appsignal.send_error($!) do |transaction|
      transaction.set_action action_name
      transaction.set_namespace "background"
    end
    Appsignal.stop "runner"
  end
end

But this way you only get error reporting, not instrumentation. Official support of rails runner would be great.