fix: package template refencing old components

[ewingjm]

Purpose

Environment variables were removed as a result of #52 but the package template still referenced these old components.

Approach

Removes references to old environment variables. Also refactored to use Capgemini/powerapps-packagedeployer-template as this already handles through configuration some of what our package template was doing through code.

TODOs

• [x] Automated test coverage for new code
• [x] Documentation updated (if required)
• [x] Build and tests successful