Allow cv_device to add configlet without listing all configlets

[titom73]

Use case:

When devices are all deployed with their configilet, it might be useful to add a new configlet to device using cv_device module.

Current module implementation requires to list all configlet and add new configlet to the list. This approach means user has to maintain list of configlets per device and run a workflow close to the rollout targeting a larger scope than just 1 device + 1 configlet

Change behaviour:

To allow user to target only one device with one configlet, it can be useful to add an option related to configlets in cv_device to support addition or deletion of a set of configlets.

Current implementation use the following syntax:

vars:
  devices_inventory:
    veos01:
    name: veos01
    configlets:
        - cv_device_test01
        - SYS_TelemetryBuilderV2_172.23.0.2_1
        - veos01-basic-configuration
        - SYS_TelemetryBuilderV2
    parentContainerName: DC1_VEOS
tasks:
    - name: "Configure devices on {{inventory_hostname}}"
      cv_device:
        devices: "{{devices_inventory}}"
        cvp_facts: '{{cvp_facts.ansible_facts}}'
        device_filter: ['veos']
      register: cvp_device

To support such change, 2 options could be implemented and both are already present in other modules

• Use a configlet filter:

With this approach, configlet filter allows user to target only configlets with a specific string. So as for cv_container it is easy to add only one configlet with following example:

vars:
  devices_inventory:
    veos01:
    name: veos01
    configlets:
        - veos01-basic-configuration
    parentContainerName: DC1_VEOS
tasks:
    - name: "Configure devices on {{inventory_hostname}}"
      cv_device:
        devices: "{{devices_inventory}}"
        cvp_facts: '{{cvp_facts.ansible_facts}}'
        device_filter: ['veos']
        configlet_filter: ['veos01-basic-configuration']
      register: cvp_device

But in case we want to remove it from this device, it is required to fallback to original definition with all configlets.

This approach is similar to filters implemented in cv_configlet

• Use a definition of mode

With implemnentation of a mode keyword, we can define 3 different behaviours:
- override (default): Completely intend based approach and will apply the full list of configlet to device and remove unlisted configlets.
- merge: Only add new configlets to existing list.
- delete: Delete list of configlets from device.

vars:
  devices_inventory:
    veos01:
    name: veos01
    configlets:
        - veos01-basic-configuration
    parentContainerName: DC1_VEOS
tasks:
    - name: "Configure devices on {{inventory_hostname}}"
      cv_device:
        devices: "{{devices_inventory}}"
        cvp_facts: '{{cvp_facts.ansible_facts}}'
        device_filter: ['veos']
        configlet_mode: merge
      register: cvp_device

This approach is similar to cv_container with its mode option

[titom73]

Work is part of PR #122