Create demo theme and APM package, and set up deploy pipeline

### Description

Build out a demo site that displays all of the out-of-the-box features of Elasticsearch Extensions so that MVP designs can be created that utilize those features (and nothing more)

- Create a new theme (in a separate repo) to showcase the Elasticsearch Extensions functionality
- Perhaps the theme should be general (e.g. `alley-demo`) so that we could add more functionality to it for other functionality we'd like to demo
- Create the APM package for the theme
- Utilize our deploy pipeline to deploy to our VIP demo site https://dashboard.wpvip.com/apps/2781/production

### Use Case

When a designer is creating designs for an search page powered by Elasticsearch, they should have a demo site to reference so that they can design components based on what Elasticsearch Extensions provides