fix #3123. support metadata xml config and support dubbo.properties format 'dubbo.metadata-report.address=XXx'

[cvictory]

1. support dubbo xml configuration. including schema and spring support.
2. In dubbo.properties the format of key should be dubbo.metadata-report.address = XXX
3. multi metadata report support

[codecov-io]

Codecov Report

Merging #3138 into 2.7.0-release will increase coverage by 0.02%.
The diff coverage is 100%.

@@                 Coverage Diff                 @@
##             2.7.0-release    #3138      +/-   ##
===================================================
+ Coverage            63.56%   63.58%   +0.02%     
  Complexity              75       75              
===================================================
  Files                  651      651              
  Lines                28150    28154       +4     
  Branches              4774     4774              
===================================================
+ Hits                 17893    17903      +10     
+ Misses                8007     8003       -4     
+ Partials              2250     2248       -2

Impacted Files	Coverage Δ	Complexity Δ
...c/main/java/org/apache/dubbo/common/Constants.java	92.85% <ø> (ø)	0 <0> (ø)	⬇️
...g/context/annotation/DubboConfigConfiguration.java	66.66% <ø> (ø)	0 <0> (ø)	⬇️
...bo/config/spring/schema/DubboNamespaceHandler.java	100% <100%> (ø)	0 <0> (ø)	⬇️
.../org/apache/dubbo/config/MetadataReportConfig.java	41.66% <100%> (+5.3%)	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)
.../exchange/support/header/HeaderExchangeServer.java	58.11% <0%> (-1.71%)	0% <0%> (ø)
...e/dubbo/remoting/transport/netty/NettyChannel.java	56.47% <0%> (-1.18%)	0% <0%> (ø)
.../apache/dubbo/remoting/transport/AbstractPeer.java	63.04% <0%> (ø)	0% <0%> (ø)	⬇️
...apache/dubbo/rpc/protocol/dubbo/DubboProtocol.java	66.66% <0%> (+0.83%)	0% <0%> (ø)	⬇️
... and 5 more

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