Suggestion-Add customized hosts and apt source settings during template building

[RenLin0630]

In some intranet scenrio, public APT source is unavailble, and there may not be public DNS service, either. so it is necesssary to optionally add hosts settings and customized APT source in orchestrator building settings.

[linear]

ENG-3404

[jakubno]

@RenLin0630 , thanks for suggestion. Make sense to me. We're open for such contribution