gbmcweb: Add Redfish BootOption PATCH (BootOptionEnabled)

Adds PATCH /redfish/v1/Systems/<id>/Boot/BootOptions/<ref>/ to enable or
disable a UEFI boot option via SystemRegistry::UpdateBootOptionEnabled.

- Only BootOptionEnabled is patchable; any other property is rejected
  with 400.
- Returns 204 No Content on success, 404 if the boot option does not exist,
  and 500 for any other registry error.

Google-Bug-Id:539554519
PiperOrigin-RevId: 995287646
Change-Id: I55015c4c8c599e2590650c144a4d6a454cd46234