Adding Sync Status

[kt-12]

All Submissions:

• Does your code follow the WooCommerce Sniffs variant of WordPress coding standards?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?
• Will this change require new documentation or changes to existing documentation?

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Changes proposed in this Pull Request:

Closes #327 .

Steps to test the changes in this Pull Request:

1. Open the products list page.
2. Do a quick edit and try to sync a product by setting Sync with Square.
3. Cause a sync to fail. I used the wrong API key.
4. Both successful and failed syncs should show up on the list page.

Changelog entry

Add - Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.

[kt-12]

I have kept @since x.x.x for now