#### Why I did it
Fixing https://github.com/Azure/sonic-buildimage/issues/8938
Fixing 1x10G DPB mode in Mellanox-SN2700-D40C8S8 SKU as it was causing sonic-cfggen to fail.
#### How I did it
Added correct mode format in hwksu.json in Mellanox-SN2700-D40C8S8 and updated platform.json for the new mode.
#### How to verify it
Using sonic-cfggen verify it works fine
#### 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