feature request: allow custom jupyter command

[chrstphrchvz]

Currently the extension is harcoded to run the command jupyter notebook:

vscodeJupyter/src/jupyterServices/notebook/factory.ts

Lines 53 to 64 in be71800

	private startJupyterNotebookInTerminal(startupFolder: string, args: string[]) {
	this.notebookOutputChannel.appendLine('Starting Jupyter Notebook');
	this.notebookOutputChannel.appendLine('jupyter ' + ['notebook'].concat(args).join(' '));
	return spanwPythonFile('jupyter', ['notebook'].concat(args), startupFolder)
	.then(proc => {
	this.proc = proc;
	this.proc.stderr.on('data', data => {
	this.notebookOutputChannel.append(data.toString());
	});
	});
	}

It would be desirable to instead use jupyter command by default while allowing a custom jupyter command as a user/workspace setting, in case one with a different name or PATH is needed. This is a feature which many other extensions tend to offer for any system commands they use.

(I'm using jupyter installed from MacPorts, which at the moment only provides renamed commands like jupyter-3.6 commands to prevent conflicts between multiple versions—one for each Python version. There is likely a way to allow selecting one of them to provide an exact jupyter command, but that still hasn't been added after quite some time: cf. https://trac.macports.org/ticket/51529.)