domains: add option to set custom/vanity nameservers

this flag skips the NS name validation when a custom nameserver is set
i.e not to the provider's NS but uses the provider's API.

dashboard/src/components/DomainDialog.vue

@@ -53,6 +53,7 @@ const zoneName = ref('');
 const provider = ref('');
 const tlsProvider = ref('letsencrypt-prod-wildcard');
 const showAdvanced = ref(false);
+const customNameservers = ref(false);
 
 const accessKeyId = ref('');
 const secretAccessKey = ref('');
@@ -118,7 +119,10 @@ async function onSubmit() {
   busy.value = true;
   errorMessage.value = '';
 
-  const config = {};
+  const config = {
+    customNameservers: customNameservers.value
+  };
+
   if (provider.value === 'route53') {
     config.accessKeyId = accessKeyId.value;
     config.secretAccessKey = secretAccessKey.value;
@@ -224,6 +228,8 @@ defineExpose({
     provider.value = d.provider || '';
     tlsProvider.value = d.tlsConfig.provider || 'letsencrypt-prod-wildcard';
 
+    customNameservers.value = d.config.customNameservers;
+
     gcdnsProjectId.value = (d.provider === 'gcdns' && d.config.projectId) || '';
     gcdnsClientEmail.value = (d.provider === 'gcdns' && d.config?.credentials.client_email) || '';
     gcdnsPrivateKey.value = (d.provider === 'gcdns' && d.config?.credentials.private_key) || '';
@@ -494,6 +500,8 @@ defineExpose({
             <TextInput id="zoneNameInput" v-model="zoneName" />
           </FormGroup>
 
+          <Checkbox v-model="customNameservers" :label="$t('domains.domainDialog.customNameservers')" />
+
           <FormGroup>
             <label for="tlsProviderInput">{{ $t('domains.domainDialog.certProvider') }} <sup><a href="https://docs.cloudron.io/certificates/#certificate-providers" class="help" target="_blank"><i class="fa fa-question-circle"></i></a></sup></label>
             <select id="tlsProviderInput" v-model="tlsProvider">