livebook server: Add --open-new flag

[wojtekmach]

No description provided.

[wojtekmach]

It removes one extra step, the click on the "New notebook" button, to get running with Livebook.

[jonatanklosko]

Beautiful 🐈

[josevalim]

I am honestly 👎. The flag only works if you don't have a server already running and I don't think the CLI noise is worth saving one click.

[jonatanklosko]

The flag only works if you don't have a server already running

So does the --open flag. I can still imagine this being useful if someone uses an alias to start Livebook, though this may be an overoptimisation 🤔

[josevalim]

Here is an alternative: if the server is already running, we show a readable error message the server is already running (we can either check the port or if there is a node with the same name on the machine), and then we open it anyway. This way someone can use livebook server --open or --open-new multiple times:

$ livebook server --open
Livebook already running. Opening it...

And if there is no open:

$ livebook server
Livebook already running at foo.bar:321.