After playing a while with the symfony configuration I realised there's no way to make symfony parse and load a yaml file if its extension is not in ['yml', 'yaml']

Shouldn't it be a configuration?

Something like:

imports:
    - { resource: my_custom_config.ext, format: yml }

I can submit a pull request

I'm sorry if this may be already implemented somehow and I'm not aware of it.

Cheers