EventGate Read Stats Lambda - no auth yet

### Feature Description

The `event_stats_lambda.py` has a separate handler and that does not implement auth.

Challenge whether a separated handler, by which I mean file `handler_stats.py`, is worth it, and if yes, add authorization as it is done in the other handler.

### Problem / Opportunity

We need to protect this endpoint as it queries the real DB.

### Acceptance Criteria

Endpoint is protected with authorization mechanism similar to the other lambda in `event_gate_lambda.py`