Self-supervised tutorial & update
- Basic tutorial for self-supervised pre-training and subsequent supervised fine-tuning
- Config for conformer SSL (may be changed later)
- Update to convert_to_tarred script to enable not having "text" field in manifest, and allow using "offset" for manifest without labels
- Add optional non-stride layers to reconstruction decoder
- Add option to load part of model from second nemo checkpoint from config (for example if we want to load encoder from one pre-trained model, and decoder from another)

# Changelog
- New way to initialize parts of models into current model for ssl

```markdown
  init_from_nemo_model: Str path to a .nemo model in order to load state_dict from single nemo file;
  if loading from multiple files, pass in a dict where the values have the following fields:
      - path: Str path to .nemo model
      - include: Optional list of strings, at least one of which needs to be contained in parameter name
      to be loaded from this .nemo file. Default: everything is included.
      - exclude: Optional list of strings, which can be used to exclude any parameter containing one of
      these strings from being loaded from this .nemo file. Default: nothing is excluded.
      hydra usage example:

```


```yaml
...

init_from_nemo_model:
    model0:
        path:<path/to/model1>
        include:["encoder"]
    model1:
        path:<path/to/model2>
        include:["decoder"]
        exclude:["embed"]

```