optimize apollo extension

[chickenlj]

What is the purpose of the change

optimize the Apollo extension of Config-Center SPI

Brief changelog

ApolloDynamicConfiguration

Verifying this change

https://github.com/apache/incubator-dubbo-samples/tree/samples-for-2.7.0-SNAPSHOT/dubbo-samples-configcenter/dubbo-samples-configcenter-apollo

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[codecov-io]

Codecov Report

Merging #3263 into 2.7.0-release will decrease coverage by 0.02%.
The diff coverage is 0%.

@@                 Coverage Diff                 @@
##             2.7.0-release    #3263      +/-   ##
===================================================
- Coverage            63.65%   63.62%   -0.03%     
  Complexity              75       75              
===================================================
  Files                  658      658              
  Lines                28538    28545       +7     
  Branches              4825     4825              
===================================================
- Hits                 18166    18163       -3     
- Misses                8095     8106      +11     
+ Partials              2277     2276       -1

Impacted Files	Coverage Δ	Complexity Δ
...ter/support/apollo/ApolloDynamicConfiguration.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../remoting/transport/netty4/NettyClientHandler.java	75% <0%> (-11.12%)	0% <0%> (ø)
...che/dubbo/remoting/transport/mina/MinaChannel.java	43.42% <0%> (-10.53%)	0% <0%> (ø)
...onfig/spring/extension/SpringExtensionFactory.java	78.04% <0%> (-7.32%)	0% <0%> (ø)
.../dubbo/remoting/transport/netty4/NettyChannel.java	61.17% <0%> (-4.71%)	0% <0%> (ø)
...e/dubbo/remoting/transport/netty/NettyChannel.java	54.11% <0%> (-3.53%)	0% <0%> (ø)
.../exchange/support/header/HeaderExchangeServer.java	58.11% <0%> (-1.71%)	0% <0%> (ø)
.../apache/dubbo/remoting/transport/AbstractPeer.java	63.04% <0%> (ø)	0% <0%> (ø)	⬇️
.../java/org/apache/dubbo/config/ReferenceConfig.java	58.08% <0%> (+0.36%)	0% <0%> (ø)	⬇️
...he/dubbo/registry/multicast/MulticastRegistry.java	65.08% <0%> (+1.29%)	0% <0%> (ø)	⬇️
... and 4 more

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[cvictory]

I have review the code and run the sample.