Adding the "env" script when --wp-env or wpEnv is present.

[ryanwelcher]

Description

As discussed in #25188 (comment), when the --wp-env flag is passed or thewpEnv is added to a template, there is no accompanying script added to the package. json.

Testing Instructions

Test locally using:

• ./node_modules/.bin/wp-create-block --wp-env to test the flag
• ./node_modules/.bin/wp-create-block --template=@ryanwelcher/dynamic-block-template to test a template using wpEnv
• ./node_modules/.bin/wp-create-block to ensure that no additional scripts are added.

Types of changes

New feature. Adds "env": "wp-env" to the package.json

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).
• I've updated related schemas if appropriate.

[gziolo]

Nice idea. It brings more consistency 👍🏻

Would you mind listing it in the CHANGELOG of the package?