Projects should support multiple artifacts

### Current Behavior

Currently, a project in Dependency-Track roughly resembles a *single* [Bill of Materials](https://cyclonedx.org/specification/overview/).

This can be limiting in the following ways:

* Some projects consist of multiple parts, and as a consequence of multiple BOMs. For example, a project may have an [HBOM](https://cyclonedx.org/capabilities/hbom/) for hardware components, one or more [SBOM](https://cyclonedx.org/capabilities/sbom/)s for software running on that hardware, and one or more [SaaSBOM](https://cyclonedx.org/capabilities/saasbom/)s that describe service components. A [CBOM](https://cyclonedx.org/capabilities/cbom/) may be added to describe cryptographic algorithms. It is not practical to create separate projects for all of these. Merging them prior to uploading them to DT is possible, but complex.
* Users currently (ab-) use project hierarchies to represent such structures. This is more complex to manage, and not necessarily how we intended hierarchies to be used.
* Supplementary artifacts such as [VEX](https://cyclonedx.org/capabilities/vex/) and [attestations](https://cyclonedx.org/capabilities/attestations/) can never represent projects on their own, by design. But users may still want to upload and track them.
* The upcoming [transparency exchange API](https://github.com/CycloneDX/transparency-exchange-api/) supports many more artifacts than just SBOMs. Currently, DT would only support a small subset of them.

### Proposed Behavior

Enable projects to ingest and track multiple artifacts.

The solution should work with DependencyTrack/dependency-track#6188, such that artifacts are bound to project *versions*.

### Checklist

- [x] I have read and understand the [contributing guidelines](https://github.com/DependencyTrack/hyades/blob/main/CONTRIBUTING.md#filing-issues)
- [x] I have checked the [existing issues](https://github.com/DependencyTrack/hyades/issues) for whether this enhancement was already requested