Add reverse proxy URL to Notification settings

Current Situation

• Users configure notifications to make use of the JOC Cockpit URL by using variables such as ${JOC_HREF_*}{}.
• The URL is specified internally from the currently used JOC Cockpit instance.
• This does not reflect the fact that users who for example receive notifications by mail might have to access JOC Cockpit from a reverse proxy URL.

Desired Behavior

• It should be possible to specify a (reverse proxy) URL instead of automatically using the current JOC Cockpit instance's URL (default).
• This setting has to be available for any MessageFragments (Command Line, Mail, JMS etc.)
• This setting is managed
  • from the JOC Cockpit Settings page with section joc and the name joc_reverse_proxy_url, for example https://joc-2-0-secondary:4446.
  • from the Notification sub-view that allows use of the following variables provided that the joc_reverse_proxy_url setting is available:
    • ${JOC_REVERSE_PROXY_HREF_JOB}
    • ${JOC_REVERSE_PROXY_HREF_JOB_LOG}
    • ${JOC_REVERSE_PROXY_HREF_ORDER}
    • ${JOC_REVERSE_PROXY_HREF_ORDER_LOG}
    • ${JOC_REVERSE_PROXY_HREF_WORKFLOW}