Spawned while investigating https://github.com/matrix-org/synapse/issues/13944
This way we might get some more context whenever an `403 Forbidden - body: {"errcode":"M_FORBIDDEN","error":"You don't have permission to access that event."}` error is produced.
`log_config.yaml`
```yaml
loggers:
synapse:
level: INFO
synapse.visibility:
level: DEBUG
```
