Add lambda DSL method for featurePolicy

[jzheaux]

Even though Permission-Policy is targeted to replace Feature-Policy, browsers still largely support Feature-Policy, not Permission-Policy. Further , Permission-Policy is still in draft.

As such, we should add the lambda DSL for featurePolicy to HeadersConfigurer and to ServerHttpSecurity. We should also consider removing deprecation markers for Feature-Policy from the Servlet, Reactive, and Kotlin DSLs.

Related #9262

[therepanic]

Hi, @jzheaux! You marked this as ideal-for-contribution, so I guess I can try to solve this issue?

[jzheaux]

For sure, @therepanic, thanks for volunteering!