MFLT-12997 better sync_memfault_successful metric

Due to how memfault data is typically sent over MQTT, the
`sync_memfault_successful` built-in (zephyr port) metric doesn't fire,
since that is set in the http uploader.

Add the metric to the MQTT Memfault data uploader.

Drive-by changes included:

- update to Memfault SDK v1.5.2
- set a default static `software_version` of `0.0.99-dev`, which should
  be overridden at OTA image build time on the command line. this helps
  distinguish dev builds from OTA builds.

overlay-memfault.conf

@@ -39,3 +39,6 @@ CONFIG_DEBUG_MODULE_MEMFAULT_HEARTBEAT_INTERVAL_SEC=3600
 # Disable NRF Cloud FOTA to save some kB, we don't use it
 CONFIG_NRF_CLOUD_FOTA=n
 CONFIG_MEMFAULT_FOTA=y
+
+CONFIG_MEMFAULT_NCS_FW_VERSION_STATIC=y
+CONFIG_MEMFAULT_NCS_FW_VERSION="0.0.99-dev"

src/modules/debug_module.c

@@ -76,7 +76,13 @@ static void memfault_internal_send(void)
 	 * Memfault SDKs internal HTTP transport is used.
 	 */
 #if !defined(CONFIG_DEBUG_MODULE_MEMFAULT_USE_EXTERNAL_TRANSPORT)
-		memfault_zephyr_port_post_data();
+	int rv = memfault_zephyr_port_post_data();
+	if (rv != 0) {
+		LOG_ERR("memfault_zephyr_port_post_data, error: %d", rv);
+	} else {
+
+	}
+	goto entry;
 #else
 	uint8_t data[CONFIG_DEBUG_MODULE_MEMFAULT_CHUNK_SIZE_MAX];
 	size_t len = sizeof(data);
@@ -89,6 +95,7 @@ static void memfault_internal_send(void)
 		message = k_malloc(len);
 		if (message == NULL) {
 			LOG_ERR("Failed to allocate memory for Memfault data");
+			memfault_metrics_connectivity_record_memfault_sync_failure();
 			goto entry;
 		}
 
@@ -106,6 +113,10 @@ static void memfault_internal_send(void)
 
 		len = sizeof(data);
 	}
+
+	// Finished submitting Memfault chunks to the MQTT QoS handler, count this
+	// as a Memfault sync success
+	memfault_metrics_connectivity_record_memfault_sync_success();
 #endif
 	goto entry;
 }

west.yml

@@ -17,7 +17,7 @@ manifest:
     - name: memfault-firmware-sdk
       url: https://github.com/memfault/memfault-firmware-sdk
       path: modules/lib/memfault-firmware-sdk
-      revision: "release/1.5.0"
+      revision: "1.5.2"
 
   self:
     path: firmware