add socks5 proxy support

[nihongye]

What is the purpose of the change

add socks5 proxy support for dubbo-remoting-netty4.

Brief changelog

Check the system property 'socks5ProxyHost' in org.apache.dubbo.remoting.transport.netty4.NettyClient#initChannel, if it exists, use the system property socks5ProxyHost and socks5ProxyPort to create a Socks5ProxyHandler and add it to the first location of the ChannelPipeline

Verifying this change

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[codecov-io]

Codecov Report

Merging #3624 into master will decrease coverage by 0.07%.
The diff coverage is 20%.

@@             Coverage Diff              @@
##             master    #3624      +/-   ##
============================================
- Coverage     63.77%   63.69%   -0.08%     
  Complexity       71       71              
============================================
  Files           712      713       +1     
  Lines         31450    31495      +45     
  Branches       5073     5076       +3     
============================================
+ Hits          20057    20061       +4     
- Misses         9103     9138      +35     
- Partials       2290     2296       +6

Impacted Files	Coverage Δ	Complexity Δ
...e/dubbo/remoting/transport/netty4/NettyClient.java	70.58% <20%> (-4.02%)	0 <0> (ø)
.../apache/dubbo/qos/protocol/QosProtocolWrapper.java	64.1% <0%> (-17.95%)	0% <0%> (ø)
...apache/dubbo/common/config/ConfigurationUtils.java	64% <0%> (-8%)	0% <0%> (ø)
...ava/org/apache/dubbo/config/DubboShutdownHook.java	75% <0%> (-6.25%)	0% <0%> (ø)
...pache/dubbo/registry/support/AbstractRegistry.java	77.39% <0%> (-4.6%)	0% <0%> (ø)
...dubbo/remoting/exchange/support/DefaultFuture.java	72.78% <0%> (-3.41%)	0% <0%> (ø)
...ommon/serialize/protostuff/utils/WrapperUtils.java	90.69% <0%> (-2.41%)	0% <0%> (ø)
.../exchange/support/header/HeaderExchangeServer.java	66.98% <0%> (-1.89%)	0% <0%> (ø)
.../apache/dubbo/remoting/transport/AbstractPeer.java	67.39% <0%> (ø)	0% <0%> (ø)	⬇️
...rialize/protostuff/delegate/TimestampDelegate.java	62.5% <0%> (ø)	0% <0%> (?)
... and 1 more

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[htynkn]

just wondering what's situation we need use socket proxy? if it's common usage, do we need apply similar change to other remoting module?

Please check the way to get SOCKS_PROXY_PORT

[zonghaishang]

Please check the way to get SOCKS_PROXY_PORT

[nihongye]

@zonghaishang replace System.getProperty to ConfigUtils.getProperty. please review again

[chickenlj]

LGTM.