esp_openthread_platform_init() function

- ESP_OK on success - ESP_ERR_NO_MEM if allocation has failed - ESP_ERR_INVALID_ARG if radio or host connection mode not supported - ESP_ERR_INVALID_STATE if already initialized

This function is not called by and will not call the OpenThread library. The user needs to call otInstanceInitSingle to initialize the OpenThread stack after calling this function.