add spring starter r2dbc support

Author: zeitlinger

instrumentation/spring/spring-boot-autoconfigure/src/main/java/io/opentelemetry/instrumentation/spring/autoconfigure/instrumentation/r2dbc/R2dbcAutoConfiguration.java

@@ -17,6 +17,9 @@
 @Conditional(SdkEnabled.class)
 @Configuration(proxyBeanMethods = false)
 public class R2dbcAutoConfiguration {
+
+  public R2dbcAutoConfiguration() {}
+
   @Bean
   static R2dbcInstrumentingPostProcessor r2dbcInstrumentingPostProcessor(
       ObjectProvider<OpenTelemetry> openTelemetryProvider) {