[Dubbo-5872] use QOS command to check if app service is ready

[Hinsteny]

What is the purpose of the change

Add one QOS command to check application is ready or not!

Brief changelog

M dubbo-config/dubbo-config-api/src/main/java/org/apache/dubbo/config/bootstrap/DubboBootstrap.java
A dubbo-plugin/dubbo-qos/src/main/java/org/apache/dubbo/qos/command/impl/Ready.java
M dubbo-plugin/dubbo-qos/src/main/resources/META-INF/dubbo/internal/org.apache.dubbo.qos.command.BaseCommand
M dubbo-plugin/dubbo-qos/src/test/java/org/apache/dubbo/qos/command/util/CommandHelperTest.java

Verifying this change

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[codecov-io]

Codecov Report

Merging #5873 into master will decrease coverage by 0.13%.
The diff coverage is 27.77%.

@@             Coverage Diff              @@
##             master    #5873      +/-   ##
============================================
- Coverage     61.33%   61.19%   -0.14%     
+ Complexity      500      496       -4     
============================================
  Files           981      982       +1     
  Lines         39147    39165      +18     
  Branches       5645     5648       +3     
============================================
- Hits          24011    23968      -43     
- Misses        12516    12561      +45     
- Partials       2620     2636      +16     

Impacted Files	Coverage Δ	Complexity Δ
.../apache/dubbo/config/bootstrap/DubboBootstrap.java	52.69% <25.00%> (-1.23%)	0.00 <0.00> (ø)
.../java/org/apache/dubbo/qos/command/impl/Ready.java	50.00% <50.00%> (ø)	0.00 <0.00> (?)
...rg/apache/dubbo/remoting/utils/PayloadDropper.java	46.15% <0.00%> (-30.77%)	0.00% <0.00%> (ø%)
...bo/config/event/listener/LoggingEventListener.java	37.50% <0.00%> (-25.00%)	0.00% <0.00%> (ø%)
...va/org/apache/dubbo/remoting/TimeoutException.java	22.22% <0.00%> (-11.12%)	0.00% <0.00%> (ø%)
...ava/org/apache/dubbo/config/DubboShutdownHook.java	65.21% <0.00%> (-10.87%)	0.00% <0.00%> (ø%)
.../apache/dubbo/rpc/protocol/AsyncToSyncInvoker.java	72.41% <0.00%> (-10.35%)	0.00% <0.00%> (ø%)
.../remoting/transport/netty4/NettyServerHandler.java	59.09% <0.00%> (-9.10%)	0.00% <0.00%> (ø%)
...e/dubbo/remoting/transport/netty/NettyChannel.java	52.27% <0.00%> (-7.96%)	19.00% <0.00%> (-2.00%)
...dubbo/remoting/exchange/support/DefaultFuture.java	79.31% <0.00%> (-6.90%)	0.00% <0.00%> (ø%)
... and 9 more

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[lkj41110]

Why is the default value not false?

[Hinsteny]

Sometimes user would not call the DubboBootstrap.start method, so then the app ready function would not working, then the app should ready in default!

[chickenlj]

I think ready should reflect more status than just checking exported services, but still, it's a good start, we can enhance it later.