caddy-frontend: New test backend features

Features:

 * random response is possible of big sizes
 * timeout can be randomized
3 jobs for feat/tesseract-version-up in 0 seconds
Status Job ID Name Coverage
  External
failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

24:02:48

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

05:43:46

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master

11:47:49