RFC: Design improved integration between DejaCode and ScanCode.io

There are a few things we need to improve in the integration between ScanCode.io and DejaCode:

- [ ] ScanCode.io should be able to be pull curated package data from DejaCode, as a preference over the PurlDB package facts. Overall, the matching would be based on PurlDB fingerprints and the base facts would be sourced from the PurlDB and DejaCode curated data would be overlaid on top.

- [ ] ScanCode.io pulling curated data could be through API lookup (or through ABOUT files TBD) for instance all the curated ABOUT files of a product.
- [ ] ScanCode.io should be able to pull the product-specific package curations from DejaCode or the dataspace-wide curations.

- [ ] DejaCode should be able to run specific pipelines in a backing ScanCode.io for a specific product (today the pipeline choice is fixed)