Support identifier on the TEA Artifact level

[taleodor]

Currently we have identifiers on the following levels:

• TEA Product
• TEA Product Release
• TEA Component
• TEA Component Release
• TEA Distribution
• CLE Event

It would make sense to also add identifiers on the TEA Artifact level with addition of BOM specific identifier types, such as serialNumber for CycloneDX or documentNamespace / spdxId for SPDX.

To implement this, we would need to:

1. Extend TEA Artifact type with list of identifiers
2. Provide API to perform direct search for TEA Artifacts based on identifier

Note: while BOM standards may assume that document identifiers are globally unique, we may not have such assumptions from the perspective of TEA (see #217 ) - therefore, we always assume that everything is essentially namespaced by a particular TEA Server, where uniqueness can actually be guaranteed.

[oej]

In my view it's a rather open-ended text string that is an alias reference or name for an artefact, in order to be able to create and resolve cross-artefact links.

IS there a need for a type or can it be just a simple string?

[oej]

One use case was to publish a large bill of materials as fragments that are linked with this identifier.