Create endpoint for Inventory

[haardikdharma10]

This PR - 


• Adds an endpoint to create an inventory item.
• Adds test for the same endpoint.
• Fixes unexpected spaces around keyword/parameter equals in models.py
• Fixes continuation line under-indented for visual indent in models.py
• Places third-party imports like "factory.fuzzy.FuzzyChoice" before first-party imports like "service.models.Inventory" to resolve PyLint checks

Fixes: https://github.com/CSCI-GA-2820-FA24-001/inventory/issues/1