Support importing templates below everything else

[Al2Klimov]

I.e.:

template Service "ssh-service" {
  import "generic-service"
  // "save" original command name, and replace it
  vars.original_check_command = check_command
  check_command = "by_ssh"
  // these get evaluated at runtime
  vars.by_ssh_command = {{ get_check_command(service.vars.original_check_command).command }}
  vars.by_ssh_arguments = {{ get_check_command(service.vars.original_check_command).arguments }}
}

apply Service "users" {
  check_command = "users"
  vars.users_wgreater = 3
  vars.users_cgreater = 5
  // ...
  import "ssh-service" // <======== HERE
}

(c) https://www.netways.de/en/blog/2016/03/21/check_by_ssh-mit-icinga-2/

Not strictly required, but very useful for check_by_ssh or Icinga/icinga2#9062.

Ideally one can even order imports. But this could be emulated with a few nested templates which import others and this below-feature.