Backwards incompatibility with notebook

[Zsailer]

I've been coming across various places where jupyter_server diverges from notebook. I'm using this issue to track these differences. This will be turned into documentation in the future to help users migrate in places where we cannot add shims.

• ConfigManager changed its config path from "nbconfig" to "serverconfig". (code)
  • Follow up question: should this be hardcoded into the config manager?

[rolweber]

Re hard-coded "serverconfig", maybe we can define an attribute that a derived ConfigManager could overwrite. Then integrators are free to implement an NbConfigManager that sets it to "nbconfig" again.

Not sure whether it would make sense to pass it as a parameter with default value to the constructor of ConfigManager.