XWIKI-12474: Make it possible to configure available syntaxes at runtime using the Admin UI

* Put back the xwiki.rendering.syntaxes property which is still useful for defining the initial list of active syntaxes

xwiki-platform-tools/xwiki-platform-tool-configuration-resources/src/main/resources/xwiki.cfg.vm

@@ -32,6 +32,13 @@
 #-# When the wiki is readonly, any updates are forbidden. To mark readonly, use one of: yes, 1, true
 # xwiki.readonly=no
 
+#-# [Since 1.6RC1] Defines the initial list of supported syntaxes. They list of enabled syntaxes is then controlled by
+#-# the Admin UI of XWiki. When not defined, the default syntax ("xwiki/2.1") is configured by default.
+#-# Example of syntaxes:
+#-#    xwiki/2.0, xwiki/2.1, confluence/1.0, jspwiki/1.0, creole/1.0,  mediawiki/1.0, twiki/1.0, xhtml/1.0,
+#-#    html/4.01, plain/1.0, docbook/4.4, markdown/1.0, markdown/1.1, apt/1.0
+#-# xwiki.rendering.syntaxes = xwiki/2.1
+
 #-# List of groups that a new user should be added to by default after registering. Comma-separated list of group
 #-# document names.
 # xwiki.users.initialGroups=XWiki.XWikiAllGroup