scsi: target: Add virtual remote target

Create virtual remote target module.

This can be used to see a whole ACL/LUN/TPG configuration from all nodes in
storage cluster. For example, it permits setting up remote ports in ALUA
port groups. To report all ports in a cluster in REPORT TARGET PORT GROUP
command.

Suggested-by: Konstantin Shelekhin <k.shelekhin@yadro.com>
Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Link: https://lore.kernel.org/r/20230313181110.20566-13-d.bogdanov@yadro.com
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>