[BUG][Bot Service] deploymentEnvironment's default value causes internal server error when try to create ms teams channel

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/main/specification/botservice/resource-manager/Microsoft.BotService/stable/2022-09-15/botservice.json#L2259

### API Spec version

2022-09-15

### Describe the bug

As defined in swagger, MsTeamsChannel has property `deploymentEnvironment` with default value `FallbackDeploymentEnvironment`.
Yet, when passing this value to create MsTeamsChannel, would receive the error from service and fail to create the channel:
```
azure.core.exceptions.HttpResponseError: (UnknownError) An unexpected error occurred. Exception: 'Newtonsoft.Json.JsonSerializationException: Error converting value "FallbackDeploymentEnvironment" to type 'Microsoft.Bot.Internal.Schema.FirstPartyChannelDeploymentEnvironment'. Path 'properties.deploymentEnvironment'. ---> System.ArgumentException: Requested value 'FallbackDeploymentEnvironment' was not found.
```

### Expected behavior

Update the swagger file to have a workable default value for property `deploymentEnvironment`.

### Actual behavior

Now we have to remove `deploymentEnvironment` from the request body to make the operation succeed.

### Reproduction Steps

Send request body with default values that defined in swagger, receive internal server error.
```
{"location": "global", "properties": {"channelName": "MsTeamsChannel", "location": "global", "properties": {"enableCalling": false, "isEnabled": true, "deploymentEnvironment": "FallbackDeploymentEnvironment"}}}
```

### Environment

_No response_

Open specification/botservice/resource-manager/Microsoft.BotService/stable/2022-09-15/botservice.json around line 2259 and inspect MsTeamsChannel.properties.deploymentEnvironment. Compare the declared default with the service's accepted values, then verify the corrected default using the reproduction request; done means creating the MS Teams channel no longer returns the conversion error.

Written by the indexing model from the issue text.