docs: add prototype sphinx extension for online help

goes through the sections in the documents and creates the
OnlineHelpInfo.js file from the explicitly defined section labels which
are used in the js files with 'onlineHelp' variable.

www/Makefile

@@ -54,6 +54,10 @@ all: js/proxmox-backup-gui.js css/ext6-pbs.css
 js:
 	mkdir js
 
+OnlineHelpInfo.js:
+	$(MAKE) -C ../docs onlinehelpinfo
+	mv ../docs/output/scanrefs/OnlineHelpInfo.js .
+
 js/proxmox-backup-gui.js: js OnlineHelpInfo.js ${JSSRC}
 	cat OnlineHelpInfo.js ${JSSRC} >$@.tmp
 	mv $@.tmp $@

www/OnlineHelpInfo.js

@@ -1,6 +1,10 @@
-var proxmoxOnlineHelpInfo = {
-    "pbs_documentation_index" : {
-	"link" : "/pbs-docs/index.html",
-	"title" : "Proxmox Backup Server Documentation Index"
-    }
+const proxmoxOnlineHelpInfo = {
+  "pbs_documentation_index": {
+    "link": "/pbs-docs/index.html",
+    "title": "Proxmox Backup Server Documentation Index"
+  },
+  "chapter-zfs": {
+    "link": "/docs/sysadmin.html#chapter-zfs",
+    "title": "ZFS on Linux"
+  }
 };