Introduce an API to customize the starter template for code components

Overview

When a new code component is created on the XB UI, there is starter code added to the component's JavaScript source to use as an example.

Different websites may want to provide different starter templates for code components. E.g., the current one uses Drupal brand colors and elements, and an organization may want to update that to something relevant to their brand.

Proposed resolution

Introduce an API to customize the starter template for code components

User interface changes