MongoDocumentStore.findDocuments can fail with BSON exception

This can happen in an edge case where the BSON condition exceeds the 16MB limit (see in test for OAK-10642).

The quick fix is to catch the exception and then use a simplified version of the method that get's the documents one-by-one.

Mid-term, we may want to refactor this so that we avoid the exception by limiting the size of the BSON condition proactively.