Adding to an AppService a mount to an inexistent Azure FileShare doesn't produce an error (but breaks the appService instance)

[0gust1]

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

Describe the bug
The following command should return an error when <FILE_SHARE_NAME> doesn't exist in the target storage account:

az webapp config storage-account add -g <RESSOURCE_GROUP_NAME> -n <APP_SERVICE_NAME> --custom-id "test-az-cli" --storage-type AzureFiles --account-name <STORAGE_ACCOUNT_NAME> --share-name <FILE_SHARE_NAME> --access-key <STORAGE_ACCOUNT_ACCESS_KEY> --mount-path <MOUNT_PATH_ON_APP_SERVICE_FS> --debug

When ran on an existing appService, the above command put the appService in a semi-broken state where Kudu become.unavailable and deployments are not working anymore

To Reproduce

• Create a storage account
• Create an appService instance
• run the above command with the right parameters and a non-existent fileshare name.
• try to deploy some code to the app, or try to ssh into it (webSSH), or try to look at deployment logs, or try to access Kudu UI (https://<appServiceInstanceName>.scm.azurewebsites.net ) : everything should fail

Expected behavior

• az webapp config storage-account add should fail / return an error when specifying an inexistent File_share.
• the endpoint of Azure management API https://management.azure.com/subscriptions/<subscriptionID>/resourceGroups/<RG_NAME>/providers/Microsoft.Web/sites/<APP_NAME>/config/azurestorageaccounts/add should return an error as well

Environment summary

• AppService Linux (Node in our case)
• we use terraform to provision our infra (but the problem was reproduced with azure-cli)

Additional context

N/A

[yonzhan]

route to CXP team