[rdf] Gitlab Prov-o-metadata step

[cristianvasquez]

Description: A prov-metadata step that produces lineage triples from Gitlab environment variables.

Motivation: For specific datasets, one would like to have links to the pipeline runs, know the name of the person that worked on the code, the Barnard pipeline itself, etc.

When a pipeline is running, one has access to the following variables:
https://docs.gitlab.com/ee/ci/variables/predefined_variables.html

One would want to add metadata related to the pipeline run. The vocabulary to model this is https://www.w3.org/TR/prov-o/.

Other related resources:

https://github.com/DLR-SC/gitlab2prov
https://github.com/DLR-SC/Gitlab2Graph

[cristianvasquez]

Related: https://academic.oup.com/gigascience/article/8/11/giz095/5611001?login=false

[cristianvasquez]

Pull request: zazuko/barnard59-rdf#31