esp_http_server: Provide apps an option to let http_server ignore sess_ctx changes

By default, if a URI handler changes the http session context,
the webserver internally clears the older context after the handler
returns. However, if applications want to change this behavior and
manage the allocation/de-allocation/freeing themselves and let the
server handle only the "socket close" case, this commit provides such
an option.

components/esp_http_server/src/esp_httpd_priv.h

@@ -60,6 +60,7 @@ struct thread_data {
 struct sock_db {
     int fd;                                 /*!< The file descriptor for this socket */
     void *ctx;                              /*!< A custom context for this socket */
+    bool ignore_sess_ctx_changes;           /*!< Flag indicating if session context changes should be ignored */
     void *transport_ctx;                    /*!< A custom 'transport' context for this socket, to be used by send/recv/pending */
     httpd_handle_t handle;                  /*!< Server handle */
     httpd_free_ctx_fn_t free_ctx;      /*!< Function for freeing the context */