Allow editing DNS-Provider credentials in the UI after initial creation

[t46g]

Is your feature request related to a problem? Please describe.:
Once you create a DNS-01 validated certificate via the UI, you cannot update its DNS provider API credentials. To change them, you must delete and recreate the certificate and change the certificate for every host which was using the old one.

Describe the solution you’d like:
Add an “Edit DNS Provider” option in the certificate UI to modify Customer Number, API Key, and API Password in place—no deletion or manual re-provisioning required.