Add exception class MDTemporarilyUnavailableException

MDErrorReporter.php

@@ -37,6 +37,7 @@ public static function categorizeError(Throwable $exception):MDErrorCategory {
             || $exception instanceof MDMysqliExpectedError
             || $exception instanceof MDcouldNotSetPublic
             || $exception instanceof MDInvalidNodaLink
+            || $exception instanceof MDTemporarilyUnavailableException
         ) {
             return MDErrorCategory::known;
         }

exceptions/generic/MDTemporarilyUnavailableException.php

@@ -0,0 +1,18 @@
+<?PHP
+declare(strict_types = 1);
+
+/**
+ * Custom exception class for presenting that a functionality is currently unavailable.
+ */
+final class MDTemporarilyUnavailableException extends Exception {
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        return 'This functionality is currently unavailable';
+
+    }
+}