Ability to acquire config file path in already started service

[DmitriyH]

Currently, there is no option to find out in already started service, which config file path was used to read server config.
But It would be useful.
For example, if there were this option, it would be possible to specify additional file paths in config, relative to config file location, regardless of process current directory.

Currently, the sample below doesn't work, but with that option would:

project_dir$ cat static_config.yaml
...
  my-service:
    data-file-path: subdir/data.json
...

project_dir$ my_service --config static_config.yaml
another_dir$ my_service --config /home/.../project_dir/static_config.yaml

A very simple solution would be:

• declare a global variable config_file_path in core/src/components/run.cpp and GetConfigFilePath function in the corresponding header to get the value
• set the variable inside ConfigToManagerVisitor::operator()(const std::string&)