Updated Dockerfile to support securing container supply chain

[compulim]

Fixes #4301

Changelog Entry

Changed

• Resolves #4301. Updated Dockerfile to support secure container supply chain, by @compulim in PR #4303

Description

Updated our Dockerfile with new ARG which can be configured via --build-arg:

Name of ARG	Description	Default
REGISTRY	Registry to pull images from, will prepend to BASE_IMAGE	docker.io
BASE_IMAGE	Qualified base image name	$REGISTRY/node:18 (for samples) $REGISTRY/node:18-alpine (for tooling)

Note: all of our images are based on node.

Design

When developing/testing/building Web Chat, this feature will help our customers to specify a different container registry, or a different base image to start with.

They can specify build arguments when building the image using Docker:

docker --build-arg REGISTRY=mycompany.azurecr.io .

Or via Compose:

docker-compose build --build-arg REGISTRY=mycompany.azurecr.io

Specific Changes

• Update all Dockerfile* with unified build arguments for retargeting base images
• Fixed screenshot of __tests__/video.js with slightly changed channel icon

• I have added tests and executed them locally
• I have updated CHANGELOG.md
• I have updated documentation

Review Checklist

This section is for contributors to review your work.

• Accessibility reviewed (tab order, content readability, alt text, color contrast)
• Browser and platform compatibilities reviewed
• CSS styles reviewed (minimal rules, no z-index)
• Documents reviewed (docs, samples, live demo)
• Internationalization reviewed (strings, unit formatting)
• package.json and package-lock.json reviewed
• Security reviewed (no data URIs, check for nonce leak)
• Tests reviewed (coverage, legitimacy)