Add Mellanox configurations and planning

1. Add Mellanox configuration in settings tab.
2. Create initial section for usign Mellanox hardware
   in the planning guide.

Partial-Bug: 1359216

Change-Id: I40de76cf61e7942850f34f16bb906d02a2a2761c
Signed-off-by: Aviram Bar-Haim <aviramb@mellanox.com>
Merge "Add Mellanox configurations and planning"