ENH: Auto look for `_polished.yml`

[muschellij2]

ENH - close if needed.

I wonder if some code could be useful that if you pass in NULL or have NULL as the default for global_sessions_config arguments, then it could look for a _polished.yml file, similar to pkgdown and bookdown.

  polished_yaml_file = "_polished.yml"
  if (file.exists(polished_yaml_file)) {
    polished_config = config::get(file = polished_yaml_file)
  }

[merlinoa]

Yes I think this could be useful. I'll give it some more thought over the next couple days.