Edit Pages domains

We can add new domains to Pages, we can see details of existing ones, but we cannot update informations.

We could want to update the public certificate as we renew it, but at that point we can also consider to allow modification of the private key.

Currently we've to remove the domain and add it again, that also implies we've the private key available at that moment.

Add the ability to edit the certificate and to upload a new private key.

Domain renewal, rekeying of certificate.

Make sure these are completed before closing the issue, with a link to the relevant commit.