enhance bundled examples

[beiwei30]

What is the purpose of the change

add more basic examples, including xml config, annotation config, and pure api, for easier debugging/self-verfication purpose.

Brief changelog

XXXXX

Verifying this change

XXXXX

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[codecov-io]

Codecov Report

Merging #3115 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #3115      +/-   ##
============================================
- Coverage     63.52%   63.49%   -0.03%     
  Complexity       75       75              
============================================
  Files           652      652              
  Lines         28183    28183              
  Branches       4791     4791              
============================================
- Hits          17902    17895       -7     
- Misses         8023     8030       +7     
  Partials       2258     2258

Impacted Files	Coverage Δ	Complexity Δ
.../remoting/transport/netty4/NettyClientHandler.java	75% <0%> (-11.12%)	0% <0%> (ø)
...e/dubbo/remoting/transport/netty/NettyChannel.java	57.64% <0%> (-4.71%)	0% <0%> (ø)
...pache/dubbo/remoting/transport/AbstractServer.java	44.79% <0%> (-4.17%)	0% <0%> (ø)
...dubbo/remoting/exchange/support/DefaultFuture.java	73.82% <0%> (-1.35%)	0% <0%> (ø)
.../java/org/apache/dubbo/config/ReferenceConfig.java	57.3% <0%> (-0.77%)	0% <0%> (ø)
.../apache/dubbo/remoting/transport/AbstractPeer.java	63.04% <0%> (+2.17%)	0% <0%> (ø)	⬇️
...he/dubbo/remoting/transport/netty/NettyServer.java	71.42% <0%> (+3.57%)	0% <0%> (ø)	⬇️
.../dubbo/remoting/transport/netty4/NettyChannel.java	65.88% <0%> (+4.7%)	0% <0%> (ø)	⬇️
...onfig/spring/extension/SpringExtensionFactory.java	85.36% <0%> (+4.87%)	0% <0%> (ø)	⬇️

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[khanimteyaz]

Is there any plan to use @Autoimport of sprint-boot or should we keep it @reference ?