[AVM Module Issue]: Storage Account - Blob Service cannot disable ChangeFeed

### Check for previous/existing GitHub issues

- [x] I have checked for previous/existing GitHub issues

### Issue Type?

Bug

### Module Name

avm/res/storage/storage-account

### (Optional) Module Version

0.32.1

### Description

It seems impossible to disable the ChangeFeed setting. I have the following code, but it is ignored.
```
blobServices: {
changeFeedEnabled: false
}
```

I suspect it's because of the way blobServices is declared. If `changeFeedEnabled` is set to false, `changeFeed` is set to null and the change is then ignored.
```
resource blobServices 'Microsoft.Storage/storageAccounts/blobServices@2025-01-01' = {
name: name
parent: storageAccount
properties: {
automaticSnapshotPolicyEnabled: automaticSnapshotPolicyEnabled
changeFeed: changeFeedEnabled
? {
enabled: true
retentionInDays: changeFeedRetentionInDays
}
: null
...
```

### (Optional) Correlation Id

_No response_