add no match placeholder for email domains

dashboard/src/views/EmailDomainsView.vue

@@ -117,6 +117,7 @@ onMounted(async () => {
       </template>
 
       <div>
+        <div v-if="filteredDomains.length === 0" class="email-placeholder">{{ $t('domains.noMatchesPlaceholder') }}</div>
         <a v-for="domain in filteredDomains" :key="domain.domain" :href="`#/email-domain/${domain.domain}`" class="email-domain">
          <div style="display: flex; align-items: center;">
             <StateLED :busy="domain.loadingStatus" :state="domain.status ? 'success' : 'danger'"/>
@@ -144,6 +145,11 @@ onMounted(async () => {
 
 <style scoped>
 
+.email-placeholder {
+  text-align: center;
+  margin-top: 150px;
+}
+
 .email-domain {
   display: flex;
   border-radius: var(--pankow-border-radius);