Add Project configuration for Lighting CMP so it can use ot_cert_coap_lib if desired (#324)

Author: jmartinez-silabs

slc/apps/zigbee-matter-light/thread/zigbee-matter-light.slcp

@@ -189,6 +189,10 @@ configuration:
     value: 16
   - name: SL_MBEDTLS_PSA_ASSUME_EXCLUSIVE_BUFFERS
     value: 1
+# Additional config when using ot_coap_cert_libs
+  - name: SL_MBEDTLS_KEY_EXCHANGE_PSK_ENABLED
+    value: 1
+    condition: [ot_coap_cert_libs]
 # series 3 requires more stack in zb stacks
   - name: SL_CLI_EXAMPLE_TASK_STACK_SIZE
     value: 1500