Go Clean template

The purpose of the template is to show how to organize a project and prevent it from turning into spaghetti code, where to store business logic so that it remains independent, clean, and extensible, how not to lose control when a microservice grows. Configuration. First, config.yml is read, then environment variables overwrite the yaml config if they match. The config structure is in the config.go. The env-required: true tag obliges you to specify a value (either in yaml, or in environment variables). For configuration, we chose the cleanenv library. It does not have many stars on GitHub, but is simple and meets all the requirements. Reading the config from yaml contradicts the ideology of 12 factors, but in practice, it is more convenient than reading the entire config from ENV. It is assumed that default values are in yaml, and security-sensitive variables are defined in ENV.