Add `testedWith` key to the Blueprint schema

[adamziel]

Choosing WordPress and PHP version for a plugin demo is tricky. On one hand, you want to use the latest versions so that your demo auto-updates with the WordPress and PHP release cycle. On the other, the new version may not play well with the plugin.

Let's solve that at the Blueprint schema level by introducing a testedWith key:

{
	"preferredVersions": {
		"php": "8.2",
		"wp": "latest"
	},
	"testedWith": {
		"php": "8.0",
		"wp": "6.7"
	},
	"steps": [
		// ...
	]
}

In this scenario, Playground would try to run the Blueprint with the latest WordPress and PHP 8.2. If that fails, it would fall back to WordPress 6.7 and PHP 8.0, since that combination is known to work well.

[bgrgicak]

What if instead of adding a new testedWith object, we would add a new value for wp versions with a name like latest-supported?

If wp is latest-supported the Blueprint compilation would loop through all plugins in the Blueprint and determine which is the latest supported WP version from the Requires at least plugin header.
The same could work for the PHP version using the Requires PHP header.

This is how the Blueprint could look like:

{
	"preferredVersions": {
		"php": "latest-supported",
		"wp": "latest-supported"
	},
	"steps": [
		// ...
	]
}