#### Why I did it
Additional file for DPB in order to support SKU SN2700-D40C8S8 on master
#### How I did it
Add hwsku.json file
#### How to verify it
Enforce "Mellanox-SN2700-D40C8S8 SKU on Master and see it works as expected, meaning:
Port 1/3 will be used as 4x10G
Port 2/4 - Not exist (blocked since 1 and 3 split to 4)
Port 7/8/9/10/23/24/25/26 will used as 100G
All other ports will be used as 2x50G
This PR should be added on top of PR:
https://github.com/Azure/sonic-buildimage/pull/6876
#### Description for the changelog
Adding hwsku.json file to SN2700-D40C8S8 SKU
