Add Scully CLI to build image

**Is your feature request related to a problem? Please describe.**
I see the default build image that comes with Amplify comes with Gatsby and Hugo.

Scully is an up and coming static site generator for Angular. We plan to use it soon. It would be nice if Amplify Console team considers adding it to the default build image. It is new and v1 was just released so perhaps not as popular yet as Gatsby and Hugo. But just putting this request here for consideration since it's the only static site generator option for Angular at this time.

In the meantime, my team will experiment with having a custom build image.

**Additional context**
- Scully website: https://scully.io/
- Example dockerfile: https://hub.docker.com/r/beeman/scully-docker/dockerfile

Start by reviewing the example Dockerfile linked in the issue and comparing it with Amplify's default build image. Confirm what is required for the Scully CLI to be available in that image, then verify that an Angular project can invoke it successfully from the default environment.

Written by the indexing model from the issue text.