merge the additional yaml config to the main yaml config

[Nikita-Levuskin]

Changelog entry

Added the ability to merge additional config to the main config

Changelog category

• New feature

Additional information

When starting a container without configs, you can specify the environment variable "YDB_CONFIG_YAML_PATCH", which should point to the config file relative to the workdir(default "ydb_data") and, if this variable is present, the additional config is combined with the main config. If there is no file specified in the environment variable, the application will not start