caddy-frontend: Implement netloc-list

JSON schema uses simple string and internal process, and caddy instances are
not kept simple and are not considered future-proof.
6 jobs for master in 0 seconds (queued for 1 second)
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:10:58

passed SlapOS.Eggs.UnitTest-Master.Python3

00:10:32

passed SlapOS.SlapRunner.ResilienceTest-Master

00:21:26

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:39:40

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

06:09:34

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

06:13:49