feat: add skip options for cache update, apt.conf.d templates, and policyrc.d

[xiaoyao9184]

This PR refactors and extends skip conditions for APT-related tasks, introducing
clear, top-level control variables with explicit defaults.
Users can now enable or disable APT operations declaratively.

New Variables:

• apt_update
  Type: bool
  Default: true
  Purpose: Controls whether to run apt-get update and related cache-refresh operations.
  Behavior: When false, apt update and apt upgrade tasks performing cache updates are skipped.

• apt_general_periodic
  Type: bool
  Default: true
  Purpose: Enables or disables management of both general and periodic apt.conf.d templates.
  Behavior: When false, no templates 10general and 10periodic rendered under /etc/apt/apt.conf.d.

Change Variables:

• apt_policy
  Type: int
  Default: 101
  Purpose: Determines whether to manage policy priorities.
  Behavior: When value < 0, skips creation of /usr/sbin/policy-rc.d.