Unable to choose subnet to avoid CIDR overlap

## Describe the bug

**Command Name**
`az aks enable-addons`

**Errors:**
```
(ServiceCidrOverlapExistingSubnetsCidr) The specified service CIDR 10.0.0.0/16 is conflicted with an existing subnet CIDR 10.0.239.0/24
Code: ServiceCidrOverlapExistingSubnetsCidr
Message: The specified service CIDR 10.0.0.0/16 is conflicted with an existing subnet CIDR 10.0.239.0/24
Target: networkProfile.serviceCIDR

```

## To Reproduce:
Steps to reproduce the behavior. Note that argument values have been redacted, as they may contain sensitive information.

- `az aks enable-addons -a monitoring -n {} -g {} --workspace-resource-id {} --subnet-name {}`

## Expected Behavior
Monitoring successfully added to AKS

## Environment Summary
```
Windows-10-10.0.19041-SP0
Python 3.8.9
Installer: MSI

azure-cli 2.30.0

```
## Additional Context

Start at the az aks enable-addons entry point and trace how --subnet-name is handled when monitoring is added. Reproduce the ServiceCidrOverlapExistingSubnetsCidr error with the documented command, then determine what behavior would let users select a non-overlapping subnet and verify that monitoring can be added successfully.

Written by the indexing model from the issue text.