CVE-2021-20329: go.mongodb.org/mongo-driver improperly validates cstrings when marshalling Go objects into BSON

Specific cstrings input may not be properly validated in the MongoDB Go Driver when marshalling Go objects into BSON. A malicious user could use a Go object with specific string to potentially inject additional fields into marshalled documents. This issue affects all MongoDB GO Drivers up to (and including) 1.5.0.