DualStack Proposal (#237)

* DualStack Proposal

Signed-off-by: Ayush Patel <patel.ayush08@gmail.com>

* Update dualstack proposal document

- Updated attribute and struct name as per discussion
- Minor formatting in proposal document

* Added a section for discussion and decisions in dualstack proposal

* Added explaination for backward compatibility in dualstack proposal

Signed-off-by: Ayush Patel <patel.ayush08@gmail.com>