Change trace level to DEBUG

In mbed-os default trace level is INFO so certificate debug traces are not shown.

Author: Kimmo Vaisanen

mbed_app.json

@@ -3,6 +3,7 @@
         "*": {
             "platform.stdio-convert-newlines": true,
             "mbed-trace.enable": 1,
+            "mbed-trace.max-level": "TRACE_LEVEL_DEBUG",
             "rtos.main-thread-stack-size": 8192
         },
         "K64F": {