Add Build System

[kaitlinbolling]

Description

We need to add a build system to the theme to allow for the compilation of scripts and styles within the theme.

Requirements

• A frontend build system based on Alley's build tool is successfully integrated into starter theme.
• The build system supports Webpack entries for compiling global styles and extending core and custom block styles.
• Block styles should be enqueued using the wp_enqueue_block_style function.

Use Case

Developers should have an easy and performant way of extending block styles as well as adding styles and scripts to the site with flexible entry points.

[kaitlinbolling]

Example of adding a global entry with some basic CSS resets: https://github.com/alleyinteractive/savageplatform/pull/31