Message `Error: Unable to infer Connect server type and setup server` not very informative

[wch]

For example:

$ rsconnect deploy shiny -n rstudioservices .
Error: Unable to infer Connect server type and setup server.

It turned out that I had added the the server without an API key, but it took me a good while to figure that out. It would save a lot of time if the error message said what the problem was, and how to fix it. (I ended up removing the server and adding it again, with the API key.)