Provide a webhook to help limit usage (control cost & scalability)

The idea would be to have an extension point where customer can take action to help control cost.
The scenario I had in mind is the following:
- I used the Daily Usage Quota and would like to have a webhook where I could take action when that limit is reached.
- That way I can run my custom process : use the Management APi to stop the Azure Function because I don't want to generate more cost for a non critical workload.

Start by reviewing the Daily Usage Quota behavior and the Management API flow described in the issue. Define how an Azure Function customer would receive a webhook when the quota is reached and use it to trigger a custom process. Done means the webhook is emitted at the quota limit and the customer can act on it to control further cost.

Written by the indexing model from the issue text.