EmbedAPI: log success requests
Log success requests using `django-structlog` and send them New Relic to know
what projects are using EmbedAPI, if they are using sphinx-hoverxref and what
version of it.
This is the minimum configuration required to start using structlog + New Relic.
If we are happy with the results we can migrate the other logs to structlog,
which should be simple, but a little tedious to do search&replace.
In the future, we can also set up django-structlog to log Celery tasks as well.
