Capsule upgrade fails with error "Parameter foreman-proxy-httpboot invalid: nil is not a valid boolean"

Issue

• Attempting to perform an upgrade from Red Hat Satellite 6.10 to Red Hat Satellite 6.11 in a Capsule fails with the error:

  Procedures::Installer::Upgrade: 2023-06-08 13:13:16 [NOTICE] [root] Loading installer configuration. This will take some time.
  2023-06-08 13:13:20 [NOTICE] [root] Running installer with log based terminal output at level NOTICE.
  2023-06-08 13:13:20 [NOTICE] [root] Use -l to set the terminal output log level to ERROR, WARN, NOTICE, INFO, or DEBUG. See --full-help for definitions.
  2023-06-08 13:13:22 [ERROR ] [root] Parameter foreman-proxy-httpboot invalid: nil is not a valid boolean
  Error during configuration, exiting                                  [FAIL]
  Failed executing LANG=en_US.utf-8 foreman-installer  --disable-system-checks, exit status 21
  --------------------------------------------------------------------------------
  Scenario [Migration scripts to Capsule 6.11.z] failed.