Add support for fabric loopback interfaces

[mikewiebe]

Addresses the following issues:

• https://github.com/CiscoDevNet/ansible-dcnm/issues/245
• https://github.com/CiscoDevNet/ansible-dcnm/issues/246
• Add support for mpls based fabric loopback interfaces

[dsx1123]

verified with VPC use cases, it works fine, but please add examples of modifying the loopback1 in the doc.

[mikewiebe]

verified with VPC use cases, it works fine, but please add examples of modifying the loopback1 in the doc.

Added the following example in the doc

## Loopback Interfaces Created During Fabric Creation
- name: Mange Fabric loopback interfaces
  cisco.dcnm.dcnm_interface:
    fabric: mmudigon-fabric
    state: merged
    config:
      - name: lo1                           # This is usually lo0 or lo1 created during fabric creation
        type: lo
        switch:
          - "192.172.1.1"                   # provide the switch where to deploy the config
        deploy: true                        # choose from [true, false]
        profile:
          admin_state: false                # choose from [true, false]
          mode: fabric                      # This must be set to 'fabric' for fabric loopback interfaces
          secondary_ipv4_addr: 172.16.5.1   # secondary ipv4 address for loopback interface
          route_tag: "100"                  # Routing Tag for the interface
          cmds:                             # Freeform config
            - no shutdown
          description: "Fabric interface managed by Ansible"

[mikewiebe]

@dsx1123 asked me to add support for another type of fabric interface so I plan to add that before we can merge this PR

[mikewiebe]

Update: After more testing I discovered that if the module uses the correct template for the loopback interfaces I don't need to add /pti?isMultiEdit=false to the path. It's sufficient to just use PUT

[mikewiebe]

@dsx1123 and @mmudigon This code is ready for review again. If there are no further comments we can merge