Implement PipelineConfig via Dataclasses + OmegaConf

[varisd]

Replace the current opuspocus.pipelines.PipelineConfig with Dataclasses for individual steps, runners, etc.
This will enable definition of "general" pipeline values (e.g., src_lang, tgt_lang) and, by default, inheriting the necessary values in the respective steps, or linking variable values between various OpusPocus objects.

OmegaConfig should make command-line pipeline parameters overwriting easier