616 domain knowledge facts rules should be loadable via the rest api

[bnouwt]

No description provided.

[Sophietje]

Two additional comments:

1. I'd recommend adding some tests for edge cases:
   a) try to load an empty string/file
   b) try and load a file with erroneous syntax
   c) try and load a file with valid syntax but that contains something that we don't support (if that's even a thing, if so we should mention it in the docs)

2. Do we support all syntax from Apache Jena's rule syntax? I saw something about the language tag somewhere. If not, we should include what syntax is supported in the documentation

[bnouwt]

Two additional comments:

1. I'd recommend adding some tests for edge cases:
   a) try to load an empty string/file
   b) try and load a file with erroneous syntax
   c) try and load a file with valid syntax but that contains something that we don't support (if that's even a thing, if so we should mention it in the docs)
2. Do we support all syntax from Apache Jena's rule syntax? I saw something about the language tag somewhere. If not, we should include what syntax is supported in the documentation

Thanks for the review @Sophietje! A lot of good comments. Regarding the above comments:

1a) Added this case to eu.knowledge.engine.reasoner.api.JenaRuleConversionTest.
1b) This is already tested in eu.knowledge.engine.rest.api.TestDomainKnowledge.testDomainKnowledge().
1c) I've added tests and logic to deal with Builtin primitives which the TKE does not support.
2) I've added a tip about language tags in the documentation 👍