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 <[email protected]>
[FE: update "Since: " from 6.2 to 7.0
     make @connected a common member of @SetPasswordOptions]
Signed-off-by: Fabian Ebner <[email protected]>
Message-Id: <20220225084949[email protected]>
Acked-by: Markus Armbruster <[email protected]>
Reviewed-by: Dr. David Alan Gilbert <[email protected]>
Signed-off-by: Dr. David Alan Gilbert <[email protected]>