Configure trusted image policy for Twistlock

Added the ability to configure a trusted registry, defaulting to match Ironbank. Also has the ability to set the "fallback policy" (i.e. for all other images) to "alert" or "block". Changes to the registry or effect will result in updates, but name changes result in a new policy.

For https://repo1.dso.mil/platform-one/big-bang/apps/security-tools/twistlock/-/issues/32