Pick up the `default-rsconnect-server` setting from RStudio Server Pro

[colearendt]

https://docs.rstudio.com/ide/server-pro/r-sessions.html#rstudio-connect-server

RStudio Server Pro makes a "Default Connect Server" setting available that is then populated in the R session whenever creating a "connection" to an RStudio Connect server for deployment.

Ideally, the rsconnect-jupyter plugin would have the same affordances, to simplify the experience for users unfamiliar with where the company's Connect server may be residing.

[samcofer]

I wanted to ping this issue as important for being able to provide a great pro experience out of the box!