Feature Request: Add API Endpoint to allow "Airlock Status Update" to be collected

The approval process for airlock imports is triggered by an event grid event, and then deliberately left vague as it something that can be implemented by a given customer.

However, in order to display the status of an airlock process, and the allow for audit/logging, it would be useful if the API exposed an endpoint that...

1. Allowed the caller to supply a string (short free text) that described the current status of the approval process
2. Stored these strings
3. Allowed the UI to retrieve these status updates

e.g. so that the following might be send/stored by the API

"Interim approval started"
"Team X has been notified"
"Team X has approved"
"Interim approval completed"

None of these status updated would be used by the API or the Airlock Processor. They are purely for logging/audit, and so that the TRE Web UI can display a status report.

Start by tracing the existing airlock approval API and the TRE Web UI flow described in the issue; no specific files or tests are named. Define how status strings are submitted, stored, retrieved, and displayed, then verify that the API and UI show an audit history without changing Airlock Processor behavior.