Enable RestClientAutoConfiguration in reactive web applications when virtual threads are enabled

[philwebb]

Currently RestClientAutoConfiguration uses NotReactiveWebApplicationCondition so that it is only enabled for non-reactive web applications which helps prevent users from accidentally blocking the event loop thread.

This foot-gun protection is less useful when virtual threads are enabled, as we configure WebFlux with an async task executor which allows blocking calls to be made for any controller method that does not return reactive types. Since RestClientAutoConfiguration provides a lot of helpful functionality, we should relax the condition to a NotReactiveWebApplicationOrVirtualThreadsEnabledCondition

[kwondh5217]

Hi @philwebb!
I'd like to contribute to this issue.

Would the following approach make sense to you?

@ConditionalOnThreading(Threading.PLATFORM)
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.REACTIVE)
private static final class ReactiveWebAppWithPlatformThread {
}

[philwebb]

Closing in favor of PR #44952. Thanks @dmitrysulman!