[ort-server] Make the primary package ID syntax configurable

sschuberth: Esp. when interacting with other compliance tools, e.g. in the context of the OCCTET project, it can be confusing for users that ORT Server is the only tool that uses ORT's package IDs to refer to packages. Instead, using package URLs (purl) probably is a better choice, esp. with purl emerging as an ECMA standard.

However, as right now quite a bit of project-specific configuration still needs to be done in one of ORT's configuration files as no UI to do the same exists, and these configuration files often need to refer to packages via ORT's IDs, also the latter should still be available for easy copying & pasting.

So the idea is to make the primary package ID that ORT Server uses throughout the UI should become configurable per user. That way, users can switch depending on their background (existing ORT users or new ORT Server users), and no screen space is "wasted" by displaying both ORT's IDs and purls in all places.

Original Issue: GitHub Issue #2176