Add linkage between Default Source and Stock being installed at the time of MSI installation (inventory module install).

Thus, Default Source is assigned to Default Stock. So, we have Up and Running Stock after Magento with MSI on board has been installed.

That will help to use MSI instead CatalogInventory in future with seamless user experience for those users who use Single Stock Magento

Read this document for more details - https://github.com/magento-engcom/msi/wiki/The-Concept-of-Default-Source-and-Domain-Driven-Design