Renovate - Add renovate for Big Bang

There are various resources in Big Bang that should be kept in sync with other repos. This issue would implement a renovate.json that would automatically create an issue/MR for these items.

Add renovate for:

• https://repo1.dso.mil/platform-one/big-bang/bigbang/-/blob/master/tests/images.txt
• https://repo1.dso.mil/platform-one/big-bang/bigbang/-/blob/master/base/flux/kustomization.yaml