Extension path in Jupyter Book extension should use context.extensionPath

[Charles-Gagnon]

Currently the jupyter book template is using the hardcoded .azuredatastudio/extensions folder as the root to search for the extension folder.

https://github.com/llali/generator-azuredatastudio/blob/main/generators/app/templates/ext-jupyterbook/src/jupyter-book.ts#L13

This is bad for a couple reasons :

1. The path might change - while that's pretty unlikely there's always the possibility we put the folder somewhere else or name it something different
2. This won't work for other versions of ADS - for example our insiders builds have a .azuredatastudio-insiders folder that extensions are installed into
3. It's unnecessary to iterate over all the other folders in that directory - that's just adding extra overhead

Instead you should use https://github.com/microsoft/azuredatastudio/blob/main/src/vs/vscode.d.ts#L5616 (which comes from the context passed to the activate function)

And so you should be able to get rid of most of this logic and just have this be in the activate function :

export function activate(context: vscode.ExtensionContext) {
    context.subscriptions.push(vscode.commands.registerCommand('launchBook.<%= name %>', () => {
        vscode.commands.executeCommand('bookTreeView.openBook', context.extensionPath, false);
    }));