Protocomm : Added new APIs for opening and closing secure sessions

New APIs:
* protocomm_open_session()
* protocomm_close_session()

This allows external applications using protocomm to manually create and close sessions.

These internally call the new_transport_session() and close_transport_session() APIs implemented by the security scheme in use.

Updated unit tests with usage of new APIs

components/protocomm/include/common/protocomm.h

@@ -114,6 +114,39 @@ esp_err_t protocomm_add_endpoint(protocomm_t *pc, const char *ep_name,
  */
 esp_err_t protocomm_remove_endpoint(protocomm_t *pc, const char *ep_name);
 
+/**
+ * @brief   Allocates internal resources for new transport session
+ *
+ * @note
+ *  - An endpoint must be bound to a valid protocomm instance,
+ *    created using `protocomm_new()`.
+ *
+ * @param[in]  pc         Pointer to the protocomm instance
+ * @param[in]  session_id Unique ID for a communication session
+ *
+ * @return
+ *  - ESP_OK : Request handled successfully
+ *  - ESP_ERR_NO_MEM : Error allocating internal resource
+ *  - ESP_ERR_INVALID_ARG : Null instance/name arguments
+ */
+esp_err_t protocomm_open_session(protocomm_t *pc, uint32_t session_id);
+
+/**
+ * @brief   Frees internal resources used by a transport session
+ *
+ * @note
+ *  - An endpoint must be bound to a valid protocomm instance,
+ *    created using `protocomm_new()`.
+ *
+ * @param[in]  pc         Pointer to the protocomm instance
+ * @param[in]  session_id Unique ID for a communication session
+ *
+ * @return
+ *  - ESP_OK : Request handled successfully
+ *  - ESP_ERR_INVALID_ARG : Null instance/name arguments
+ */
+esp_err_t protocomm_close_session(protocomm_t *pc, uint32_t session_id);
+
 /**
  * @brief   Calls the registered handler of an endpoint session
  *          for processing incoming data and generating the response