Add ServerWebExchange getter in WebFlux Observation context

The observation context relies on request and response for propagation,
but the exchange itself holds attributes and locale context so this is
needed for keyvalues extraction in general.

This commit adds a getter to expose the exchange from the context.

spring-web/src/main/java/org/springframework/http/observation/reactive/ServerRequestObservationContext.java

@@ -35,6 +35,8 @@ import org.springframework.web.util.pattern.PathPattern;
  */
 public class ServerRequestObservationContext extends RequestReplyReceiverContext<ServerHttpRequest, ServerHttpResponse> {
 
+	private final ServerWebExchange serverWebExchange;
+
 	@Nullable
 	private PathPattern pathPattern;
 
@@ -42,10 +44,18 @@ public class ServerRequestObservationContext extends RequestReplyReceiverContext
 
 	public ServerRequestObservationContext(ServerWebExchange exchange) {
 		super((request, key) -> request.getHeaders().getFirst(key));
+		this.serverWebExchange = exchange;
 		setCarrier(exchange.getRequest());
 		setResponse(exchange.getResponse());
 	}
 
+	/**
+	 * Return the current {@link ServerWebExchange HTTP exchange}.
+	 */
+	public ServerWebExchange getServerWebExchange() {
+		return this.serverWebExchange;
+	}
+
 	/**
 	 * Return the path pattern for the handler that matches the current request.
 	 * For example, {@code "/projects/{name}"}.