DESEC: implement ListZones (#2381)

Co-authored-by: Tom Limoncelli <tlimoncelli@stackoverflow.com>

providers/desec/desecProvider.go

@@ -248,3 +248,12 @@ func (c *desecProvider) GetZoneRecordsCorrections(dc *models.DomainConfig, exist
 
 	return corrections, nil
 }
+
+// ListZones return all the zones in the account
+func (c *desecProvider) ListZones() ([]string, error) {
+	var domains []string
+	for domain := range c.domainIndex {
+		domains = append(domains, domain)
+	}
+	return domains, nil
+}