samples: net: cellular_modem: include at shell

Include new AT shell alongside the PM device shell to allow
for powering back up the modem after the sample has completed
to test out the at shell.

Signed-off-by: Bjarki Arge Andreasen <bjarki@arge-andreasen.me>

Author: bjarki-andreasen

samples/net/cellular_modem/prj.conf

@@ -30,6 +30,11 @@ CONFIG_MODEM_CELLULAR=y
 CONFIG_MODEM_STATS=y
 CONFIG_SHELL=y
 
+# Testing
+CONFIG_MODEM_AT_SHELL=y
+CONFIG_PM_DEVICE_SHELL=y
+CONFIG_SHELL_WILDCARD=n
+
 # Logging
 CONFIG_LOG=y
 CONFIG_MODEM_MODULES_LOG_LEVEL_DBG=y