Align use of arc_specification package

[Brilator]

1. Where do I find the arc_specification validation packages (e.g. arc_specification: 2.0.0-draft)
2. I'd suggest to list them in https://avpr.nfdi4plants.org/packages
3. I'd suggest to align the validation of ARCs with those of other packages, e.g.

instead of

arc_specification: 2.0.0-draft
validation_packages:
  - name: invenio
    version: 2.1.0

do

validation_packages:
  - name: arc_specification
    version: 2.0.0-draft
  - name: invenio
    version: 2.1.0

[kMutagene]

Spec validation is handled differently from packages. In contrast to packages, which have to be scripts that are executed in isolation, we decided to have the spec validation as a direct part of the core arc-validate tool. That has the advantage that we can do way more extensive testing on those validation cases. To reflect this correctly in the config file, specs are not a part of the package section.

You can find the code for spec validation here: https://github.com/nfdi4plants/arc-validate/tree/main/src/ARCExpect/SpecificationValidation