feat: add timestamp during product prep to track sync latency

[rithikb24]

Description

To enhance latency tracking, a new field, product_prepare_time, will be added. This field will record the Unix timestamp when a product is prepared for synchronization with the Facebook catalog.

All synchronization go through prepare_product() function. This modification will enable the tracking of time elapsed from product preparation until its appearance in the Facebook/Meta catalog, allowing for latency health monitoring.

Motivation Doc for more comprehensive explanation

The changes are very similar to - #2973
If there were any concerns/issues post that change, please let me know

Type of change

• New feature (non-breaking change which adds functionality)

Checklist

✅ I have commented my code, particularly in hard-to-understand areas, if any.
✅ I have added tests (if necessary) and all the new and existing unit tests pass locally with my changes. (Tests Action Success Run)
✅ I have completed dogfooding and QA testing, or I have conducted thorough due diligence to ensure that it does not break existing functionality.

Changelog entry

Todo

Test Plan

Automated testing

Tests Action Success Run)

Manual testing

• Verified that Batch API requests include the new field and a correct timestamp value after adding a product.
• Triggered a CSV upload and confirmed the presence of the new field in the Batch API request.
• Observed feed upload results, with a CSV created for the feed (P1870450808).
• A PasteBin URL (P1864804075) displays the request with the new field.

[facebook-github-bot]

@rithikb24 has imported this pull request. If you are a Meta employee, you can view this in D78345034.