Automatically open a webservices-infra PR when a Hackbot agent's deploy infra shape changes #7219

Terraform in webservices-infra builds the Hackbot agent infrastructure from hackbot/tf/modules/resources/agents.json. We generate that file with hackbot-deploy manifest from each agent's [deploy] table in hackbot.toml. Getting a change there is still manual: someone has to notice the shape changed, regenerate the file and open the infra PR.