feat: add subtext formatter (#10400)

Co-authored-by: Jiralite <33201955+Jiralite@users.noreply.github.com>

packages/formatters/src/formatters.ts

@@ -569,6 +569,16 @@ export function unorderedList(list: RecursiveArray<string>): string {
 	return listCallback(list);
 }
 
+/**
+ * Formats the content into a subtext.
+ *
+ * @typeParam Content - This is inferred by the supplied content
+ * @param content - The content to wrap
+ */
+export function subtext<Content extends string>(content: Content): `-# ${Content}` {
+	return `-# ${content}`;
+}
+
 /**
  * Formats a date into a short date-time string.
  *