Add UPGRADE_PACKAGES for Debian-based templates

[alexellis]

Description

Add UPGRADE_PACKAGES for Debian-based templates

Motivation and Context

The UPGRADE_PACKAGES build_arg will invoke an apt upgrade to help with warnings generated from CVE / image scanners.

How Has This Been Tested?

Example:

version: 1.0
provider:
  name: openfaas
  gateway: https://openfaas.o6s.io
functions:
  updated:
    lang: python3-http-debian
    handler: ./updated
    image: ttl.sh/updated:latest
    build_args:
      UPGRADE_PACKAGES: "1"

Toggling UPGRADE_PACKAGES with 1/0 or true/false results in a rebuild and updated packages for the positive case.

Additionally, the Alpine templates support the same behaviour:

version: 1.0
provider:
  name: openfaas
  gateway: https://openfaas.o6s.io
functions:
  updated-flask:
    lang: python3-flask
    handler: ./updated-flask
    image: ttl.sh/updated-flask:latest

    build_args:
      UPGRADE_PACKAGES: "1"
      ADDITIONAL_PACKAGE: "curl"

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

An update will be needed in the docs