Add functionality to write audit log to file

For self hosted installations that may have issues with network access for e.g. webhooks, it can be useful to write the current audit log records to a file so they can be ingested as part of an existing monitoring setup.

In terms of formatting, we should write the logs in key value pairs to make it easier to ingest and parse the logs into whatever logs tool being used e.g.

action=feature_created, feature_name=ui_version, enabled=true, feature_value=1.0.0, user=user123@org.com

we should also include timestamp metadata along with the environment / project / organisation in which it occurred