gpio_new_flex_glitch_filter() function

- ESP_OK: Allocate a flex glitch filter successfully - ESP_ERR_INVALID_ARG: Allocate a flex glitch filter failed because of invalid arguments (e.g. wrong GPIO number, filter parameters out of range) - ESP_ERR_NO_MEM: Allocate a flex glitch filter failed because of out of memory - ESP_ERR_NOT_FOUND: Allocate a flex glitch filter failed because the underlying hardware resources are used up - ESP_FAIL: Allocate a flex glitch filter failed because of other error

"flex" means the filter parameters (window, threshold) are adjustable. It's independent with pin glitch filter. See also `gpio_new_pin_glitch_filter`. The created filter handle can later be deleted by `gpio_del_glitch_filter`.