unused connectionManager in RestProtocol

[finalcola]

What is the purpose of the change

Configured PoolingHttpClientConnectionManager in RestProtocol may not work.

PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
        // 20 is the default maxTotal of current PoolingClientConnectionManager
        connectionManager.setMaxTotal(url.getParameter(CONNECTIONS_KEY, HTTPCLIENTCONNECTIONMANAGER_MAXTOTAL));
        connectionManager.setDefaultMaxPerRoute(url.getParameter(CONNECTIONS_KEY, HTTPCLIENTCONNECTIONMANAGER_MAXPERROUTE));

        if (connectionMonitor == null) {
            connectionMonitor = new ConnectionMonitor();
            connectionMonitor.start();
        }
        connectionMonitor.addConnectionManager(connectionManager);
// ...
CloseableHttpClient httpClient = HttpClientBuilder.create()
                .setKeepAliveStrategy((response, context) -> {
                    HeaderElementIterator it = new BasicHeaderElementIterator(response.headerIterator(HTTP.CONN_KEEP_ALIVE));
                    while (it.hasNext()) {
                        HeaderElement he = it.nextElement();
                        String param = he.getName();
                        String value = he.getValue();
                        if (value != null && param.equalsIgnoreCase(TIMEOUT_KEY)) {
                            return Long.parseLong(value) * 1000;
                        }
                    }
                    return HTTPCLIENT_KEEPALIVEDURATION;
                })
                .setDefaultRequestConfig(requestConfig)
                .setDefaultSocketConfig(socketConfig)
                .build();

Configured PoolingHttpClientConnectionManager is used by connectionMonitor, but not set to HttpClient, which may cause a problem.

Brief changelog

XXXXX

Verifying this change

XXXXX

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[codecov-io]

Codecov Report

Merging #4614 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #4614      +/-   ##
============================================
+ Coverage     64.16%   64.16%   +<.01%     
  Complexity      452      452              
============================================
  Files           768      768              
  Lines         32873    32874       +1     
  Branches       5181     5181              
============================================
+ Hits          21093    21094       +1     
+ Misses         9363     9360       -3     
- Partials       2417     2420       +3

Impacted Files	Coverage Δ	Complexity Δ
...g/apache/dubbo/rpc/protocol/rest/RestProtocol.java	68.21% <100%> (+0.24%)	0 <0> (ø)	⬇️
...onfig/spring/extension/SpringExtensionFactory.java	78.04% <0%> (-7.32%)	0% <0%> (ø)
.../apache/dubbo/remoting/transport/AbstractPeer.java	58.69% <0%> (-4.35%)	0% <0%> (ø)
...he/dubbo/registry/multicast/MulticastRegistry.java	67.87% <0%> (-1.81%)	0% <0%> (ø)
...g/apache/dubbo/registry/consul/ConsulRegistry.java	61.87% <0%> (-0.63%)	29% <0%> (ø)
.../java/org/apache/dubbo/config/ReferenceConfig.java	59.85% <0%> (+0.36%)	0% <0%> (ø)	⬇️
...pache/dubbo/registry/support/AbstractRegistry.java	80.07% <0%> (+1.53%)	0% <0%> (ø)	⬇️
...ache/dubbo/remoting/p2p/support/AbstractGroup.java	56.81% <0%> (+11.36%)	0% <0%> (ø)	⬇️

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[beiwei30]

LGTM.