Spec: Add DANM use case to the CNF Testbed

Topic: Add DANM enabled examples to the CNF Testbed

Idea: to show Network Management w/ tenant networks and cluster networks
- manage networks in a K8s-native way
- network resource management (lower level) API
- test on Layer 3 to ensure separation
- a missing element on K8s networking
- no applications should have access to physical resources
- to replace the "SR-IOV use case" idea (rename https://github.com/cncf/cnf-testbed/milestone/36 to remove SR-IOV)

Brainstorming and use case discussion: https://docs.google.com/document/d/1VaF59CRVStx7kxH7X9Y-ltxnpzmlsqTF1PEBUEEYLkc/edit#

Reference links:
- https://github.com/nokia/danm
- https://github.com/nokia/danm/releases
- https://wiki.akraino.org/display/AK/Gerrit+Code+Repository+Overview
- https://www.nokia.com/networks/solutions/edge-cloud/