Fix versatile regex

[CFarcy]

On the PostgisSource model, the field db_host is using a custom regex as validator build with URLValidator

HOST_REGEX = (
    rf"(?:{URLValidator.ipv4_re}|{URLValidator.ipv6_re}|{URLValidator.host_re})"
)

If I understand correctly, this was made to validate URL withtout :// (which is mandatory in django URLValidator).

It create an issue with the regex being different between django version. As it is use directly as validator, it create diff in django migration when changing python version.

    db_host = models.CharField(
        max_length=255,
        validators=[RegexValidator(regex=HOST_REGEX)],
    )

In order to ensure stable behavior with multiple version of django, this part has been removed as a quick solution.
dd5b08a

One of the solution could be to create a CustomURLValidator from URLValidator and override the __call__ method to only validate the url and skip the scheme validation part.

cf: https://github.com/django/django/blob/main/django/core/validators.py#L117