Convert doc generation vocabularies action

[dannymandel]

@datadavev These are the changes to run the vocabulary markdown generation directly from the vocabularies repo via the GitHub Action. Note that I haven't seen it run successfully, but develop fails the same way as my branch does.

[dannymandel]

My branch output:

Created /github/workspace/build/docs/vocabularies since it didn't exist.
Generating markdown docs
Successfully wrote doc file to /github/workspace/build/docs/vocabularies/mat_materialsvocabulary.md
Successfully wrote doc file to /github/workspace/build/docs/vocabularies/sf_sampledfeaturevocabulary.md
Successfully wrote doc file to /github/workspace/build/docs/vocabularies/spec_specimentypevocabulary.md

[dannymandel]

Develop doc output:

mkdir -p build/docs/vocabularies
python tools/vocab2md.py src/vocabularies/materialtype.ttl > build/docs/vocabularies/materialtype.md
python tools/vocab2md.py src/vocabularies/sampledfeature.ttl > build/docs/vocabularies/sampledfeature.md
python tools/vocab2md.py src/vocabularies/specimentype.ttl > build/docs/vocabularies/specimentype.md

[dannymandel]

Manually confirmed that the contents of the files in the GH workflow match what I get when I run locally.