Add the ability to support custom network policies via a values file

We need a way for consumers to be able to add in their own flavors of network policies at the values-level by either establishing a way for them to add the policies at the package level or at the big bang template level.

Gitlab-Runner is one of the packages that currently supports this feature by allowing consumers to add in additional policies via gitlabRunner.values.networkPolicies.additionalPolicies

Below is one example of how it is currently utilized as well as what the current template code looks like.

https://repo1.dso.mil/big-bang/bigbang/-/blame/master/tests/test-values.yaml?ref_type=heads?ref_type=heads&page=2#L1653

https://repo1.dso.mil/big-bang/product/packages/gitlab-runner/-/blob/main/chart/templates/bigbang/networkpolicies/egress-runner-jobs.yaml?ref_type=heads