F force merge

Summary

Precondition for caosdb-crawler#47 (closed). Adds a force option to the merge_entities function that, instead of raising merge conflicts, overwrites the properties and attributes of entity A in case of conflicts.

Focus

Few changes in the merge_entities function and new unit test. Make sure that the default bahavior didn't change.

Test Environment

Unit tests should be sufficient.

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CHANGELOG.md

@@ -25,6 +25,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   th above `empty_diff` function). Formerly this would have caused a merge
   conflict if the referenced record(s) were identical, but stored in different
   Python objects.
+* `apiutils.merge_entities` now has an optional `force` argument (defaults to
+  `False`, i.e., the old behavior) which determines whether in case of merge
+  conflicts errors will be raised or the properties and attributes of entity A
+  will be overwritten by entity B.
 
 ### Deprecated ###