Make the upstream DocumentManager more customizable

[jtpio]

Currently the docManager.open method is patched here to be able to open documents in new browser tabs:

notebook/packages/docmanager-extension/src/index.ts

Lines 29 to 58 in 9507aa2

	// patch the `docManager.open` option to prevent the default behavior
	const docOpen = docManager.open;
	docManager.open = (
	path: string,
	widgetName = 'default',
	kernel?: Partial<Kernel.IModel>,
	options?: DocumentRegistry.IOpenOptions
	): IDocumentWidget | undefined => {
	const ref = options?.ref;
	if (ref === '_noref') {
	docOpen.call(docManager, path, widgetName, kernel, options);
	return;
	}
	const ext = PathExt.extname(path);
	let route = 'edit';
	if (
	(widgetName === 'default' && ext === '.ipynb') ||
	widgetName === 'Notebook'
	) {
	route = 'notebooks';
	}
	let url = `${baseUrl}${route}/${path}`;
	// append ?factory only if it's not the default
	if (widgetName !== 'default') {
	url = `${url}?factory=${widgetName}`;
	}
	window.open(url);
	return undefined;
	};
	}

Ideally we could instead provide another IDocumentManager to the system which would extend the base DocumentManager, but override the open method and define the current logic there.