Add flag to sort APIGroups in output

[aLekSer]

This way the resulted file would be the same each CI run for instance.

The issue with more details could be found here: googleforgames/agones#1690

The workaround for my use case would be to sort the output before making decisions was something updated or not.

[ahmetb]

Ack. Shouldn't be a flag. I assumed we're already sorting the package names and type names.