[PLG] Marketplace

[matmair]

### Closed Alpha

### Public Beta

### Horizon 

Summary

Enables two-way syncs between different marketplaces / online shops and InvenTree. This mainly concerns inventory and orders but has options to also sync (stripped down) customer accounts.
It could be extended to also handle notifications, customer info portal or shipping.

Meta

Current State: Prototype
Alpha Available: tbd
Repo Public: tbd
Code Public: Planned, tbd
Project Tracking: https://mjmair.atlassian.net/jira/software/projects/PLGMKP/boards/3