Update initial form for IP trunk creation

The input form for creating a new IP trunk is now a three-step process, where side A and B are steps 2 and 3.

• It is no longer possible to select the same device for both sides.
• The min number of links is enforced as a required amount of inputs.

@simone.spinelli the input step enforces IPTRUNK_MINUMUM_LINKS to be the exact amount of links that should be added. Is this intended behaviour?

gso/products/product_blocks/__init__.py

+from enum import IntEnum
+
+
+class PhyPortCapacity(IntEnum):
+    ONE = 1
+    TEN = 10
+    HUNDRED = 100
+    FOUR_HUNDRED = 400