We don't want users to be able to configure a maxSize for oplog truncation. 

• We were thinking to keep the internal server knob with our default sizes chosen, but confirm with someone from Atlas that customers can't configure this (maybe just not being in UI).
• We may need to revisit what the defaults should be and if we still want some internal size minimum here
• Evaluate additional guardrails around setting size (e.g. replSetResizeOplog)