ctrl: Introduce cmd SET subscriber.create <imsi>

Create a new subscriber from CTRL, similar to VTY command
"imsi IDENT create".

On success SET_REPLY contains the ID of the newly created subscriber.

Related: SYS#5993
Change-Id: Id1b760cd07712245a0eeabaac7891bce93c1fe8e

include/osmocom/hlr/logging.h

@@ -11,6 +11,7 @@ enum {
 	DMSLOOKUP,
 	DLU,
 	DDGSM,
+	DCTRL,
 };
 
 extern const struct log_info hlr_log_info;