* OVH DNS Provider (#143)
This adds the OVH Provider along with its documentation.
Unfortunately we can't set this DNS provider to support `CanUsePTR`,
because OVH only supports setting PTR target on the Arpa zone.
* OVH Registrar provider (#143)
This implements OVH as a registrar provider.
Note that NS modifications are done in a "best effort" mode, as the
provider doesn't wait for the modifications to be fully applied
(the operation that can take a long time).
* Allow support for dual providers scenarios
Since OVH released their APIv6, it is now possible to update
zone apex NS records, opening the door to complete dual providers
scenarii.
This change implements apex NS management in an OVH zone.
