Add taskfile and dev dockerfile

[jeffreyparker]

Description

I created this taskfile and dockerfile for my own local development, to help with running unit tests/etc with the exact required version of PHP and other dependencies.

Taskfiles are a simpler alternative to makefiles. It does require the separate runner tool installed, but this is also simple enough that the commands could be manually copy/pasted/ran without it. The commands all run in a multistage dockerfile so that specific stages can be run while still sharing previous stages.

Motivation and Context

This may be useful for other developers to ensure a consistent/reproducible development environment

How Has This Been Tested?

Locally verified

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)