fix: Update SnapWP environment variables

[Swanand01]

What

This PR updates the env variables shown in the admin panel.

Why

Currently snapwp-helper uses outdated env variables.

They need to be what's expected in our starter: https://github.com/rtCamp/headless/blob/develop/frontend/examples/nextjs/starter/.env.example

Related Issue(s):

How

The missing variables are added to the VariableRegistry, and the old ones updated.
A commented property is added to the variables, which is used to determine if the variable declaration line is commented in the env file preview shown in the admin panel.

Testing Instructions

Go to GraphQL > SnapWP in the WordPress admin panel.

Screenshots

Additional Info

Checklist

• I have read the Contribution Guidelines.
• My code is tested to the best of my abilities.
• My code passes all lints (PHPCS, PHPStan, ESLint, etc.).
• My code has detailed inline documentation.
• I have added unit tests to verify the code works as intended.
• I have updated the project documentation accordingly.

[Swanand01]

@justlevine / @Ta5r Does this approach look good? If yes, I'll update the tests next.

[justlevine]

Did a quick first pass re the formatting and to get some clarification about your commented approach.

Pinged @Ta5r to review and assist.

[justlevine]

Did some cleanup + formatting changes in my last commit, accidentally invalidating @Ta5r 's tests 😬.

Fix those tests (again, apologies) and this should be ready to merge

[Swanand01]

Did some cleanup + formatting changes in my last commit, accidentally invalidating @Ta5r 's tests 😬.

Fix those tests (again, apologies) and this should be ready to merge

No worries, we'll fix the tests.

[Swanand01]

@justlevine This PR is now ready for a final review/merge.