Simplify EditorChoice config retrieval

Updated the way the `EditorChoice` configuration value is retrieved. Instead of using `Configuration.GetSection("Post:Editor").Get<EditorChoice>()`, it now uses `Configuration.GetValue<EditorChoice>("Post:Editor")`. This change simplifies the retrieval process by directly getting the value of the specified type from the configuration.

src/Moonglade.Web/Pages/Admin/EditPost.cshtml

@@ -21,7 +21,7 @@
 }
 
 @section meta {
-    <meta name="editor-choice" content="@(Configuration.GetSection("Post:Editor").Get<EditorChoice>().ToString().ToLower())" />
+    <meta name="editor-choice" content="@(Configuration.GetValue<EditorChoice>("Post:Editor").ToString().ToLower())" />
     <meta name="warn-slug-modification" content="@Model.ViewModel.WarnSlugModification.ToString().ToLower()" />
 }