Context

Currently, there is an authenticator field on the mongo.endSessionOp struct. However, we never set the authenticator, so it's effectively unused. On a previous PR, Copilot pointed out that we should set the authenticator. Setting an authenticator can cause a human-in-the-loop blocking operation in the case that auth needs to be rotated, resulting in a blocking "endSessions" call. Ending sessions is generally best-effort in drivers, so it's OK for an endSession to fail sometimes rather than blocking.

Definition of done

• Remove the authenticator field from the mongo.endSessionOp struct.
• Remove all associated code.

Pitfalls

See here: https://github.com/mongodb/mongo-go-driver/pull/2512#discussion_r3660634600