qapi/monitor: allow VNC display id in set/expire_password

qapi/monitor: allow VNC display id in set/expire_password

It is possible to specify more than one VNC server on the command line,
either with an explicit ID or the auto-generated ones à la "default",
"vnc2", "vnc3", ...

It is not possible to change the password on one of these extra VNC
displays though. Fix this by adding a "display" parameter to the
"set_password" and "expire_password" QMP and HMP commands.

For HMP, the display is specified using the "-d" value flag.

For QMP, the schema is updated to explicitly express the supported
variants of the commands with protocol-discriminated unions.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
[FE: update "Since: " from 6.2 to 7.0
     make @connected a common member of @SetPasswordOptions]
Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
Message-Id: <20220225084949.35746-4-f.ebner@proxmox.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>