Fixes: FRMW-2968
In this PR we have done two major things.
- First, we remove storing CSV contents within the workflow storage and neither store the JSON payloads to be created/updated in workflows. Earlier, they all were workflow inputs, hence were stored in the workflow
- Introduce a naive concept of chunks and process chunks one by one. The next PR making chunking a bit more robust while using streams, adding ability to resume from the failed chunk and so on.
> [!IMPORTANT]
> The new endpoint `/admin/product/imports` is not in use yet. But it will be after the next (final) PR.
## Old context in workflow storage

## New context in workflow storage
