Add a CLI flag to override the custom Zarf variables

[YrrepNoj]

Right now we can define custom variables for the components that gets templated to the manifests/helm charts that the component uses. Currently, the value has to be defined in the zarf.yaml when the package is built.

An example of custom component variables is in this example

kind: ZarfPackageConfig
metadata:
  name: component-variables
  description: "Test component to demonstrate script timeout feature"

components:
  # Demonstrates injecting custom variables into a K8s resource, e.g. ###ZARF_DOG###
  - name: variable-example
    required: true
    variables:
      dog: "woof"
      cat: "meow"
    manifests:
      - name: variable-example-configmap
        files:
          - simple-configmap.yaml

It would be very useful to be able to provide the values for the custom variables during runtime. Something like zarf package deploy --values dog=woof2.

NOTE: Right now the custom variables are component specific, this means that (at the current moment at least) the custom variable names do not need to be unique throughout that package. That might need to change depending on how the solution to this issue gets implemented.

[YrrepNoj]

When this feature request was being discussed, it was pointed out that this feature would make it a lot easier to to rotate around passwords and certs of deployed packages.

[jeff-mccoy]

I think https://www.terraform.io/language/values/variables#variable-definition-precedence has a lot of well-established patterns around doing runtime based variable overrides.

[dsmithbauer]

Lol. We were just discussing the need for this exact feature again today on my team. I had even searched the open issues earlier this morning before this was written. I'd love to see this feature implemented as it would save having to repackage just to change some variables and eliminate the need to maintain different packages for different targets where the only difference is a few variables too. +1

[anoncam]

@jeff-mccoy this you have access to this, I'll be finding the appropriate ones for a zarf initial set of modules and open source that repo