Create omop2obo-fake.sssom.tsv

[matentzn]

@hrshdhgd

This mapping file should fail because it is missing prefixes, but it does not. It produces some default output and I don't understand at a cursory glance how. Can we make sure that a case like this, where prefixes are used but not declared, fails?

This should be done generically, maybe as part of #21