feat(notification): add admin rest management and deletion

Add revision-safe service and template APIs, channel mapping, and validated admin controls.

Ref: IT-1601

HrynCo.NotificationService.Web/Views/AdminTemplates/Edit.cshtml

@@ -86,7 +86,7 @@
                 <div class="template-preview-section-title">Rendered subject</div>
                 <div id="previewSubject" class="template-preview-subject"></div>
                 <div class="template-preview-section-title mt-3">Rendered HTML</div>
-                <iframe id="previewHtmlFrame" class="template-preview-frame" sandbox="" referrerpolicy="no-referrer" title="Email HTML preview"></iframe>
+                <iframe id="previewHtmlFrame" class="template-preview-frame" sandbox="allow-same-origin" referrerpolicy="no-referrer" title="Email HTML preview"></iframe>
                 <div class="template-preview-section-title mt-3">Rendered text</div>
                 <pre id="previewText" class="template-preview-text mb-0"></pre>
             </div>
@@ -98,5 +98,6 @@
     <a id="cancelTemplate" href="@Url.Action("Index", "AdminTemplates", new { serviceId = Model.ServiceId, key = Model.KeyFilter })" class="btn btn-secondary">Cancel</a>
 }
 @section Scripts {
+    <script src="~/js/email-template-preview.js" asp-append-version="true"></script>
     <script src="~/js/email-template-editor.js" asp-append-version="true"></script>
 }