[Modeling] Release a 615M English -> HBS Open-NLLB checkpoint

[gordicaleksa]

Our goal is to release an open-source, 3.3B, dense checkpoint that does machine translation for 202 languages from the NLLB project.

To get to that point let's first start by releasing OSS checkpoints with smaller scale and smaller language scope.

The goal here will be to release a model with following properties:

• (small scale) 615 M parameters
• (smaller language scope) Support only translation from English into HBS (Croatian, Bosnian, Serbian, Montenegrin).