[AVM Module Issue]: subscriptionsLimit on product cant be set to unlimited

### Check for previous/existing GitHub issues

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

### Issue Type?

Bug

### Module Name

avm/res/api-management/service

### (Optional) Module Version

/product:0.2.3

### Description

it says to omit the param to allow unlimited subscription, but due to the default alue, this will then be set to 1 or?

in https://github.com/Azure/bicep-registry-modules/blob/main/avm/res/api-management/service/product/main.bicep
```
@sys.description('Optional. Whether the number of subscriptions a user can have to this product at the same time. Set to null or omit to allow unlimited per user subscriptions. Can be present only if subscriptionRequired property is present and has a value of false.')
param subscriptionsLimit int = 1
```

### (Optional) Correlation Id

_No response_