DRIVERS-1641: pre-4.4 mongos writeConcernError does not determine retryability

[jmikola]

https://jira.mongodb.org/browse/DRIVERS-1641

Also clarify that pre-4.4 writeErrors[].code should never be used to determine retryability. This is intentionally untested because failCommand does not provide a way to mock writeErrors.

POC: https://github.com/mongodb/mongo-c-driver/pull/1501

Patch build: https://spruce.mongodb.com/version/65a19aa461837db75d4d8efe/tasks (4.2-replica-auth and 4.2-sharded-auth are the relevant tasks).

---

Please complete the following before merging:

• [x] Update changelog.
• [x] Make sure there are generated JSON files from the YAML test files.
• [x] Test changes in at least one language driver.
• [x] Test these changes against all server versions and topologies (including standalone, replica set, sharded clusters, and serverless).

[jmikola]

Reverting to draft until I can address DRIVERS-2802.