Allow 0.0.0.0 host in endpoint property

[eastandwestwind]

Our validator lib does not allow 0.0.0.0 in a url:

>>> from validators import url as is_valid_url
>>> is_valid_url("http://0.0.0.0/health")
ValidationFailure(func=url, args={'value': 'http://0.0.0.0/health', 'public': False})

But it will allow localhost and other local addresses

>>> is_valid_url("http://localhost:8080/health")
True
>>> is_valid_url("http://127.0.0.1/health")
True
>>> is_valid_url("http://127.0.0.0/health")
True

We will be sending 0.0.0.0 from fidesops, so let's specifically allow for this in fideslog