Introduce instance_name field into xrdp.ini and xrdp-sesrun, along with

the N policy in sesman.ini, allowing xrdp sessions to be tagged with an
instance name to enable persistent association with a specific
xrdp instance, to allow experiences where users reconnect to specific
sessions based on e.g. the xrdp listening port used.

docs/man/sesman.ini.5.in

@@ -235,6 +235,8 @@ Alternatively combine one-or-more of the following options
 \fBD\fR - Sessions are separated by initial display size
 .HP 4
 \fBI\fR - Sessions are separated by IP address
+.HP 4
+\fBN\fR - Sessions are separated by an instance name specified on startup
 .RE
 
 .IP

docs/man/xrdp.ini.5.in

@@ -28,6 +28,15 @@ The options to be specified in the \fB[Globals]\fR section are the following:
 Specify the port(s) that xrdp should listen on. More instructions and
 examples can be found within xrdp.ini itself.
 
+.TP
+\fBinstance_name\fR=\fI<arbitrary-string>\fR
+Specify an arbitrary name for the xrdp instance that can be used to
+identify sessions that this xrdp instance started, or which were
+spun up with the same name using \fBxrdp-sesrun\fR. When using the
+\fBN\fR policy in \fBsesman.ini\fR these sessions are kept distinct
+and can be reconnected to by connecting to the respective \fBxrdp\fR
+instance.
+
 .TP
 \fBvmconnect\fR=\fI[true|false]\fR
 (Hyper-V VMs only). Enables a wider support of security protocols when a