Release 6.20.0: Introduced command-line parameter to switch off portal (--access-denied-portal)

[changerequest]

Fix for bug #19455 requires to introduce a new command-line parameter to switch off portal (--access-denied-portal).

Please consider the different semantic than other command-line on/off options. If turned on, the portal is off. This is required for consistency reasons.

Option description:
--access-denied-portal: Denies portal access (Default is off)