feat(environment): allow to specify container runtime environment variables

[claimableperch]

Description

As described on the npmjs.org page.

Change Log

• Added support for { wp: env: { ... } } in php runtime environment (the running container environment).

Types of changes (if applicable):

• 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 not work as expected).