feat(esp_htttps_ota): handle case if server retured 304 not_modified during ota

This commit handles case for response code 304 (NOT_MODIFIED) during ota.

Closes https://github.com/espressif/esp-idf/issues/14839

components/esp_http_client/include/esp_http_client.h

@@ -208,6 +208,7 @@ typedef enum {
     HttpStatus_MovedPermanently  = 301,
     HttpStatus_Found             = 302,
     HttpStatus_SeeOther          = 303,
+    HttpStatus_NotModified       = 304,
     HttpStatus_TemporaryRedirect = 307,
     HttpStatus_PermanentRedirect = 308,
 
@@ -230,6 +231,7 @@ typedef enum {
 #define ESP_ERR_HTTP_CONNECTING         (ESP_ERR_HTTP_BASE + 6)     /*!< HTTP connection hasn't been established yet */
 #define ESP_ERR_HTTP_EAGAIN             (ESP_ERR_HTTP_BASE + 7)     /*!< Mapping of errno EAGAIN to esp_err_t */
 #define ESP_ERR_HTTP_CONNECTION_CLOSED  (ESP_ERR_HTTP_BASE + 8)     /*!< Read FIN from peer and the connection closed */
+#define ESP_ERR_HTTP_NOT_MODIFIED       (ESP_ERR_HTTP_BASE + 9)     /*!< HTTP 304 Not Modified, no update available */
 
 /**
  * @brief      Start a HTTP session