Big Bang needs a script that renders all templates for a big bang deployment

Motivation

It can be difficult at times to identify how changes at the Big Bang umbrella level can eventually make their way into the actual templates applied to the cluster. A script that does the hard work of identifying packages, collecting helm resources, then rendering templates with the correct values based on Big Bang's configuration would go a long way toward improving the testability of Big Bang.

Functional Requirements

• A script must be created that templates Big Bang as well as all the enabled packages
• The script must take overlays as arguments the same way a helm install/upgrade command would to allow easily using it as a surrogate or "test run" for installs and upgrades
• The script must be able to fetch helm charts for rendering from git and helm sources
• The script must overlay values the same way a flux install of packages would

Nonfunctional Requirements

• The script must be composed of simple commands that are part of the "core" kubernetes toolset (yq, jq, helm, etc.; no gum please)
• The script must conform to shellcheck and shfmt linting rules