[ticket/15735] Add posting_preview_content_after template event

Needed for extensions who adds information at the end of the message
(such as moderator messages).

PHPBB3-15735

phpBB/docs/events.md

@@ -1707,6 +1707,13 @@ posting_poll_body_options_after
 * Since: 3.1.4-RC1
 * Purpose: Add content after the poll options on creating a poll
 
+posting_preview_content_after
+===
+* Locations:
+    + styles/prosilver/template/posting_preview.html
+* Since: 3.2.4-RC1
+* Purpose: Add content after the message content preview
+
 posting_preview_poll_after
 ===
 * Locations:

phpBB/styles/prosilver/template/posting_preview.html

@@ -31,6 +31,8 @@
 
 		<div class="content">{PREVIEW_MESSAGE}</div>
 
+		<!-- EVENT posting_preview_content_after -->
+
 		<!-- IF .attachment -->
 		<dl class="attachbox">
 			<dt>{L_ATTACHMENTS}</dt>