docs: add short initial http-proxy docs

better than nothing and something to point to in the UI

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

docs/package-repositories.rst

@@ -178,3 +178,19 @@ snipped
   :caption: File: ``/etc/apt/sources.list``
 
   deb http://download.proxmox.com/debian/pbs-client buster main
+
+.. _node_options_http_proxy:
+
+Repository Access Behind HTTP Proxy
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Some setups have restricted access to the internet, sometimes only through a
+central proxy. You can setup a HTTP proxy through the Proxmox Backup Server's
+web-interface in the `Configuration -> Authentication` tab.
+
+Once configured this proxy will be used for apt network requests and for
+checking a Proxmox Backup Server support subscription.
+
+Standard HTTP proxy configurations are accepted, `[http://]<host>[:port]` where
+the `<host>` part may include an authorization, for example:
+`http://user:pass@proxy.example.org:12345`

www/OnlineHelpInfo.js

@@ -67,6 +67,10 @@ const proxmoxOnlineHelpInfo = {
     "link": "/docs/package-repositories.html#package-repositories-client-only-apt",
     "title": "APT-based Proxmox Backup Client Repository"
   },
+  "node-options-http-proxy": {
+    "link": "/docs/package-repositories.html#node-options-http-proxy",
+    "title": "Repository Access Behind HTTP Proxy"
+  },
   "get-help": {
     "link": "/docs/introduction.html#get-help",
     "title": "Getting Help"