Add unit tests for imported products

Added unit tests for the imported_* products: both the create_imported_* and import_* workflows are now tested, and the fixtures have been updated so these kinds of products can now also be used in other tests.

Test coverage up from ~80% to 92%

test/workflows/iptrunk/test_create_imported_iptrunk.py

 import pytest
 from orchestrator.types import SubscriptionLifecycle
-from products import ProductName
 
+from gso.products import ProductName
 from gso.products.product_blocks.iptrunk import IptrunkType, PhysicalPortCapacity
 from gso.products.product_types.iptrunk import ImportedIptrunk
 from test.workflows import (