Support Self-mappings for OCL imports

[jamlung-ri]

Currently, it appears that we cannot import a mapping that has the same concept as the "from" and "to" concepts. There are use cases that require this, however.

Example mapping from a bulk import file that should be supported:
{"type":"Mapping","map_type":"Associated Observations","to_concept_url":"/orgs/Regenstrief-Institute/sources/LOINC-3/concepts/81323-8/","from_concept_url":"/orgs/Regenstrief-Institute/sources/LOINC-3/concepts/81323-8/","source":"LOINC-3","owner_type":"Organization","owner":"Regenstrief-Institute"}

[jamlung-ri]

I was able to import a self-mapping in QA. Link: https://app.qa.openconceptlab.org/#/orgs/Regenstrief-Institute/sources/LOINC-3/mappings/572811/

Just for fun, I also imported fake mappings into QA that included concepts that were not part of the source, and these seemed to work well too. Link: https://app.qa.openconceptlab.org/#/orgs/Regenstrief-Institute/sources/LOINC-3/mappings/?q=&isTable=true&isList=false&isSplit=false&page=1&exactMatch=off