[Service Team Request] CLI support needed for New LB backend format

**Resource Provider**
Networking (NRP)

**Description of Feature or Work Requested**
CLI changes to support newly added Create/Update operation for backend pool and format.

**Minimum API Version Required**
2020-04-01

**Swagger Link**
Here is the PR link : https://github.com/Azure/azure-rest-api-specs/pull/8993

**Target Date**
May-end ( Manganese end).
