[11.x] Add missing roundrobin transport driver config

[u01jmg3]

• Add missing roundrobin transport driver config
  • Similar to [11.x] Add missing roundrobin transport driver config laravel#6392
• Sync configs with laravel/laravel

[taylorotwell]

Not sure why some stuff was removed like the Markdown stuff.

[driesvints]

@u01jmg3 to provide some context: the config files in framework and skeleton aren't mapped one by one. Some options like the markdown one are removed in skeleton because they're rarely changed. Options are merged together with the config files in framework.

If you want, feel free to send the round robin change separately to framework. Thanks!

[u01jmg3]

Thanks @driesvints - appreciate the context.

PR #51400 raised 🙏🏻