"az extension add --name aks-preview" in airgap cloud attempts to connect to aka.ms

> ### `az feedback` auto-generates most of the information requested below, as of CLI version 2.0.62

**Describe the bug**
An execution of "az extension add --name aks-preview" in airgap cloud, a connection attempts to reach out to aka.ms where is public url, it definitely failed.

Are aks-preview features unavailable in airgap cloud and sovereign cloud (mooncake and fairfax)?

Response
```
Unable to get extension index.

Please ensure you have network connection. Error Detail: HTTPSConnectionPool (host='**aka.ms**', port=443): Max retries exceeded with url: /azure-cli-extension-index-v1 (Caused by NewConnectionError(urllib3.connection.HTTPSConnection object 0x7fc65ca70dd8>: Failed to establish a new connection [Errno -2] Name or service not known.
```

**To Reproduce**

**Expected behavior**

**Environment summary**
az-cli 2.17.1

**Additional context**