To make it possible to index the `from` and `to` fields with
Elasticsearch and other tools, we need the types to be the same.
Currently they are a mix of boolean and string values.
Part of https://gitlab.com/gitlab-org/gitlab-ee/issues/12599
This will add audit_json.log that writes one line per audit event. For
example:
{
"severity":"INFO",
"time":"2018-10-17T17:38:22.523Z",
"author_id":3,
"entity_id":2,
"entity_type":"Project",
"change":"visibility",
"from":"Private",
"to":"Public",
"author_name":"John Doe4",
"target_id":2,
"target_type":"Project",
"target_details":"namespace2/project2"
}
