Fix Product Syncing via Feeds

[mshymon]

Changes proposed in this Pull Request:

The current state of the product syncing via Feeds is broken - while plugin code base has business logic to generate feed file daily and serve the feed file on request, there is no logic for triggering a feed one time upload.

In this PR I am suggesting the following fixes to unblock product sync via feeds:

1. Trigger a daily feed upload sessions.

   • Sending a one time create feed upload request to Meta would happen on feed file generation completion (this is to ensure we upload as feed file fresh data as possible).
   • Added logic of choosing or creating the correct feed to which such feed upload would happen. This included local caching of the integrated feed ID, validating it is valid, choosing a feed from catalog or creating a new one.

2. Update Feed file content by:

   • Adding GTIN to the feed file
   • Adding quantity_to_sell_on_facebook to the feed file

Detailed test instructions:

1. Unit Tests
   A. Run new tests:
   • ./vendor/bin/phpunit --filter ApiTest
   • ./vendor/bin/phpunit --filter fbproductTest
     B. Run all tests:
   • npm run test:php
2. Manual Tests.
   • Steps were added via an internal dogfooding doc and requires access to Meta internal tools to validate feed upload sessions status.

Changelog entry

Fix - Fixed feeds by requesting a feed file upload session after feed file is generated and added missing new fields to the feed file.