feat(bcachefs): initial implementation of bcachefs.

[iwanbk]

Fixes #2374 The goal is not to have working implementation. But to give clearer picture about what we have to do to support bcachefs, code wise.

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Checklist

• [ ] Tests included
• [ ] Build pass
• [ ] Documentation
• [ ] Code format and docstring

[iwanbk]

This PR might not be needed if we want to implement bcachefs differently from the start.

[xmonader]

before going there, these concerns need to be addressed https://github.com/threefoldtech/zos/issues/2074