Env: Allow skipping setting a configuration value by specifying it as null.

[dd32]

Fixes #41083

What?

This PR allows for wp-env to have a config configuration value skipped, if defined as null.

For example, this would result in the wp-config.php NOT containing WP_ENVIRONMENT_TYPE despite it defaulting to local in wp-env.

{
	"config": {
		"WP_ENVIRONMENT_TYPE": null
	}
}

Why?

Under some edge-cases, it may be wanted to skip setting a constant, as that makes it difficult to perform unit testing which may vary depending on it's value.

Given this constant is for a function that cannot be filtered, not having a way to avoid it being set results in unit testing pain.

Simply running wp config delete CONSTANT cannot be used for unit testing purposes either, due to the special phpunit-wp-config.php that is created, which wp-cli cannot operate on.

How?

While there might be real reasons to set a constant to false or an empty string, I can't see the need to set one to null. Skipping the constant in the case of null seems reasonable to me.

Another possibility is that for null keys, it should be a wp config delete command that is run instead. But that seemed like it was solving something that wasn't yet a problem.

Testing Instructions

1. Create a config as exampled above
2. Run wp-env start
3. Inspect configuration files, verify constant not present.

Screenshots or screencast

[noahtallen]

Makes sense to me 👍

[noahtallen]

Could you add a changelog entry before merging?

[noahtallen]

This unfortunately needs a rebase now for it to be merged :(

[dd32]

@noahtallen I think that'll take care of it.

[mburridge]

Added the Needs Dev Note label in case this needs a dev note (either individual or as part of a "misc" dev note) for WP 6.1 release.