gptimer_set_alarm_action() function

- ESP_OK: Set alarm action for GPTimer successfully - ESP_ERR_INVALID_ARG: Set alarm action for GPTimer failed because of invalid argument - ESP_FAIL: Set alarm action for GPTimer failed because of other error

This function is allowed to run within ISR context, so you can update new alarm action immediately in any ISR callback. If `CONFIG_GPTIMER_CTRL_FUNC_IN_IRAM` is enabled, this function will be placed in the IRAM by linker, makes it possible to execute even when the Flash Cache is disabled. In this case, please also ensure the `gptimer_alarm_config_t` instance is placed in the static data section instead of in the read-only data section. e.g.: `static gptimer_alarm_config_t alarm_config = { ... };`