Notice of upcoming deprecation for Boolean 'is-' properties

[octylFractal]

See gradle/gradle#22218 for full details, but the TL;DR is that Boolean (not boolean) is- properties will no longer be supported by Gradle in 9.0. This affects users of this plugin who use Groovy buildscripts to get e.g. RecommendationProviderContainer#isStrictMode. One of two things must be done:

• Introduce a new method that starts with get instead of is which has the same behavior. The old method may be removed, but be aware that doing so may break backward compatibility.
• Or change the type of the property to boolean.