samples: net: openthread: coap: add Secure Storage backend when using PSA

When PSA Crypto API are used they need a PSA ITS implementation and this
is provided by Secure Storage if TF-M is not enabled in the build.
Secure Storage on its side need a backend where to physically store data.
This commit enables ZMS as backend for samples.

Signed-off-by: Valerio Setti <[email protected]>

Author: valeriosetti

samples/net/openthread/coap/prj.conf

@@ -26,3 +26,7 @@ CONFIG_OPENTHREAD_XPANID="11:11:11:11:22:22:22:22"
 CONFIG_OPENTHREAD_NETWORKKEY="00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff"
 CONFIG_OPENTHREAD_CHANNEL=15
 CONFIG_OPENTHREAD_NETWORK_NAME="OpenThreadDemo"
+
+# Use ZMS as storage backend for Secure Storage
+CONFIG_SECURE_STORAGE_ITS_STORE_IMPLEMENTATION_ZMS=y
+CONFIG_ZMS=y