Webhooks upon server shutdown or startup

### Enhancement Type

A completely new feature

### Describe the enhancement

The ability to call a webhook with a JSON payload upon server shutdown or start up. This would be useful for a status message in something like Discord.

No file or test entry point is named in the issue, so first trace how the image handles server startup and shutdown. Define the webhook request and JSON payload for both lifecycle events, then verify that each event sends the expected status message.

Written by the indexing model from the issue text.