Provide support for WebFlux-based management endpoints

[philwebb]

No description provided.

[kuhnroyal]

A very basic approach without security:

import org.springframework.boot.actuate.autoconfigure.ManagementServerProperties
import org.springframework.boot.actuate.endpoint.AbstractEndpoint
import org.springframework.boot.context.properties.EnableConfigurationProperties
import org.springframework.context.ApplicationContext
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.http.MediaType.APPLICATION_JSON
import org.springframework.web.reactive.function.server.ServerResponse
import org.springframework.web.reactive.function.server.body
import org.springframework.web.reactive.function.server.router
import reactor.core.publisher.toMono

@Configuration
@EnableConfigurationProperties(ManagementServerProperties::class)
class ActuatorRoutes(
  private val properties: ManagementServerProperties,
  private val ctx: ApplicationContext
) {
  @Bean
  fun actuatorRouter() = router {
    (properties.contextPath and accept(APPLICATION_JSON)).nest {
      ctx.getBeansOfType(AbstractEndpoint::class.java).forEach { _, v ->
        GET("/" + v.id, { _ -> ServerResponse.ok().json().body(v.invoke().toMono()) })
      }
    }
  }
}