Enhance Nexus CI test with push/pull from Docker Registry

Package Merge Request

Package Changes

Adds a script test + config to setup a docker registry and test push/pull with it.

Package MR

https://repo1.dso.mil/platform-one/big-bang/apps/developer-tools/nexus/-/merge_requests/64/pipelines

For Issue

Closes https://repo1.dso.mil/platform-one/big-bang/apps/developer-tools/nexus/-/issues/41