Update master/slave to primary/secondary

[ParetoOptimalDev]

As many projects begin to update their api's to remove slave/master and many github repos are named main it feels a bit odd using api's that still use it for me. At the very least it's a reminder of the discussions about the terminology.

Additionally, mongodb has tickets like this one to modernize terminology and update these terms.

I can see an argument in waiting for mongodb to update those things first, but created this issue anyway because:

• It's uncomfortable
• I've had students and coworkers I was teaching that were either uncomfortable with it or at least distracted enough to ask why the API still had slave/master

What are your thoughts?