Zarf development script and documentation

General MR

Summary

This adds a script to make it easier to test Zarf out on Big Bang.

Relevant logs/screenshots

N/A

docs/guides/airgap-zarf/README.md

+# Airgap w/Zarf
+
+> ⚠️ This is a work in-progress.
+
+> ⚠️ These instructions work specifically with Big Bang version 1.54.0.  Other versions are not yet supported.
+
+This section is currently purely devoted to building and testing packages on a development cluster.  The result could be a set of archives that can be used for moving across an airgap.  Essentially this automates a few of the steps indicated in this [documentation](https://github.com/defenseunicorns/zarf/blob/main/docs/13-walkthroughs/5-big-bang.md).
+
+The first step would be to stand up a Big Bang dev cluster.  This is most easily represented by following the steps outlined here, but would ultimately result in running the below command, which stands up a larger development cluster.
+
+```shell
+source bigbang/docs/assets/scripts/developer/k3d-dev.sh -b
+```
+
+Be sure to export your Registry1 credentials next as seen below:
+
+```shell
+export REGISTRY1_USERNAME=<username>
+export REGISTRY1_CLI_SECRET=<password>
+```
+
+Now you can execute the following: 
+
+```shell
+scripts/zarf-dev.sh
+```
+
+The above will clone the latest  `main` branch of the [defenseunicorns/zarf](https://github.com/defenseunicorns/zarf) repository and execute the stock `examples/big-bang/zarf.yaml`.  If you want to use a different `zarf.yaml`, you can override this by setting any of these variables ahead of time, either by exporting them or setting them as part of the command.
+
+* `ZARF_TEST_REPO`: sets the repository to clone from.
+* `ZARF_TEST_REPO_BRANCH`: sets the branch to switch to from the cloned repo.
+* `ZARF_TEST_REPO_DIRECTORY`: sets the directory where the desired `zarf.yaml` is.
+
+Also since this all uses the same dev script, you should be able to use whatever k8s tooling (such as `kubectl` or `k9s`) you already might use on a dev cluster as `KUBECONFIG` is still transferred locally and available.