Generate and publish JavaDoc reference documentation for the generated v2.x model classes

[pmonks]

Previously (in Spdx-Java-Library v1.x), model classes had JavaDocs generated as part of that library's own JavaDoc generation and publication process. With the separation of model classes out of Spdx-Java-Library, there is no longer any JavaDoc reference documentation for these classes, yet they represent a majority (by volume) of the classes available to, and potentially used by, downstream developers. For those unfamiliar with the SPDX specification, let alone how it maps to the generated Java classes, such documentation is invaluable.

Note: it wasn't clear to me which repository this issue actually belongs in - please feel free to move it if this is the wrong one.

[bact]

This workflow https://github.com/spdx/spdx-java-model-2_X/blob/main/.github/workflows/docs.yml
already published https://spdx.github.io/spdx-java-model-2_X/

But we need to advertise the URL somewhere.

[pmonks]

Yeah I didn't find that, but that hosted instance is great! As you say we just need to link it somewhere - perhaps in the README of this project, in addition to the README of Spdx-Java-Library?

[bact]

@pmonks please review #27 thank you