Track code version and pipelines used to index a package

We need to track the code version and pipelines used to index a package.
Why? As we are updating the purldb with new features we may have indexed packages with various version of the tools and all its dependency tree. We need to decide when to rerun an indexing scan.

We have many ways to solve this:
- do nothing and just reindex/recollect single things or everything as needed as is done today. This is possibly problematic at our scale

- track which version of ScanCode.io, purldb and which pipelines has been used.
- Store in Package
- Or store in Package history

This would then be used to decide if a package needs reindexing given the current context of SCIO version, pipeline and so on. If different from the current one, we would need reindexing/recollecting.

See also https://github.com/nexB/purldb/issues/221