2022
https://www.baeldung.com/spring-boot-application-configuration
    ConfigurableServletWebServerFactory, port number
2020
https://springframework.guru/spring-external-configuration-data/
    https://habr.com/ru/company/otus/blog/576910/
https://spring.io/blog/2020/04/23/spring-tips-configuration
    SpringApplicationBuilder, !!!
????
https://spring.io/guides/gs/spring-boot/
    ApplicationContext