Add migration guide from IDF 4 to IDF 5

Related to espressif#227

Add a migration guide for transitioning from IDF 4 to IDF 5 for esp-aws-iot.

* **Migration Guide**:
  - Add a new file `MigrationGuide_IDF4_to_IDF5.md` with detailed steps and examples for migrating from `aws_iot_mqtt_client.c` to coreMQTT.
  - Include sections on updating dependencies, configuration, code, network context, callback functions, testing, and documentation.

* **README Update**:
  - Add a link to the new migration guide in the `README.md` file.
  - Update the `README.md` file to mention the availability of the new migration guide.

MigrationGuide_IDF4_to_IDF5.md

@@ -0,0 +1,79 @@
+# Migration Guide from IDF 4 to IDF 5 for esp-aws-iot
+
+This guide provides detailed steps and examples for migrating applications using functions in `aws_iot_mqtt_client.c` to the new coreMQTT component. Follow the instructions below to ensure a smooth transition.
+
+## 1. Update Dependencies
+
+Ensure that your project is using the latest version of the coreMQTT library. Update your project's dependencies to include coreMQTT.
+
+## 2. Update Configuration
+
+Update your project's configuration to use coreMQTT. This may involve updating your project's `sdkconfig` file or other configuration files.
+
+## 3. Update Code
+
+### 3.1 Replace `aws_iot_mqtt_client.c` Functions
+
+Replace the functions in `aws_iot_mqtt_client.c` with their equivalents in coreMQTT. Below are some examples of common function replacements:
+
+**Old Code Snippet**:
+```c
+aws_iot_mqtt_init(&mqttClient, &mqttInitParams);
+aws_iot_mqtt_connect(&mqttClient, &connectParams);
+aws_iot_mqtt_subscribe(&mqttClient, topic, topicLen, qos, messageHandler, pData);
+aws_iot_mqtt_publish(&mqttClient, topic, topicLen, &params);
+aws_iot_mqtt_disconnect(&mqttClient);
+```
+
+**New Code Snippet**:
+```c
+MQTT_Init(&mqttContext, &networkContext, &mqttCallbacks, &mqttBuffer);
+MQTT_Connect(&mqttContext, &connectInfo, &willInfo, timeoutMs, &sessionPresent);
+MQTT_Subscribe(&mqttContext, &subscriptionList, subscriptionCount, packetId);
+MQTT_Publish(&mqttContext, &publishInfo, packetId);
+MQTT_Disconnect(&mqttContext);
+```
+
+### 3.2 Update Network Context
+
+Update the `NetworkContext` struct to match the new coreMQTT requirements. Below is an example of the changes:
+
+**Old Code Snippet**:
+```c
+NetworkContext_t networkContext;
+networkContext.pParams = &tlsParams;
+```
+
+**New Code Snippet**:
+```c
+NetworkContext_t networkContext;
+networkContext.pParams = &transportParams;
+```
+
+### 3.3 Update Callback Functions
+
+Update any callback functions to match the new coreMQTT function signatures. Below is an example of the changes:
+
+**Old Code Snippet**:
+```c
+void messageHandler(AWS_IoT_Client *pClient, char *topicName, uint16_t topicNameLen, IoT_Publish_Message_Params *params, void *pData) {
+    // Handle message
+}
+```
+
+**New Code Snippet**:
+```c
+void eventCallback(MQTTContext_t *pContext, MQTTPacketInfo_t *pPacketInfo, MQTTDeserializedInfo_t *pDeserializedInfo) {
+    // Handle event
+}
+```
+
+## 4. Test and Validate
+
+After making the necessary changes, thoroughly test your application to ensure that it works correctly with the new coreMQTT component. Validate that all functionality is working as expected.
+
+## 5. Update Documentation
+
+Update any relevant documentation to reflect the changes made during the migration process. This may include updating README files, user guides, or other documentation.
+
+By following these steps, you can successfully migrate your application from IDF 4 to IDF 5, transitioning from `aws_iot_mqtt_client.c` to the new coreMQTT component.

README.md

@@ -190,3 +190,6 @@ Cell marked as ![alt text][supported] denotes supported combination.
 IDF version support for esp-aws-iot releases is based on [IDF Release Support Schedule](https://github.com/espressif/esp-idf#esp-idf-release-support-schedule).  
 For example, support for IDF v4.4 for Release 202406.01-LTS will expire on 31st July 2024.
 
+## Migration Guide
+
+For detailed steps and examples on migrating from IDF 4 to IDF 5 for applications using functions in `aws_iot_mqtt_client.c` to the new coreMQTT component, refer to the [Migration Guide from IDF 4 to IDF 5](MigrationGuide_IDF4_to_IDF5.md).