Add a ApiCommandHandler which fetch all registered CommandHandlers so that user can get all available CommandHandlers by request /api

[all4you]

Describe what this PR does / why we need it

Add a ApiCommandHandler which fetch all registered CommandHandlers so that user can get all available CommandHandlers by request /api

Does this pull request fix one issue?

No. Only add new features

Describe how you did it

Create a new CommandHandler called ApiCommandHandler

Describe how to verify it

1. Run Application in sentinel-demo-command-handler module
2. Request 127.0.0.1:8080/init to init the Sentinel and CommandCenter
3. Request 127.0.0.1:8719/api to get all the available CommandHandlers

[codecov-io]

Codecov Report

Merging #491 into master will increase coverage by 0.53%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #491      +/-   ##
============================================
+ Coverage     37.66%   38.19%   +0.53%     
- Complexity     1099     1114      +15     
============================================
  Files           259      259              
  Lines          8159     8173      +14     
  Branches       1111     1113       +2     
============================================
+ Hits           3073     3122      +49     
+ Misses         4690     4643      -47     
- Partials        396      408      +12

Impacted Files	Coverage Δ	Complexity Δ
...mmand/handler/FetchClusterClientConfigHandler.java	0% <ø> (ø)	0 <0> (ø)	⬇️
.../command/handler/FetchTopParamsCommandHandler.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...mmand/handler/ModifyServerNamespaceSetHandler.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...ler/ModifyClusterParamFlowRulesCommandHandler.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...mand/handler/FetchClusterMetricCommandHandler.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...mmand/handler/FetchClusterServerConfigHandler.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...d/handler/FetchClusterFlowRulesCommandHandler.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...mand/handler/ModifyClusterClientConfigHandler.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...nd/handler/ModifyParamFlowRulesCommandHandler.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...ler/ModifyClusterServerTransportConfigHandler.java	0% <ø> (ø)	0 <0> (ø)	⬇️
... and 11 more

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[sczyh30]

And please reformat your code using the Alibaba P3C plugin.

[sczyh30]

Maybe it's better to add an example to show how to register a customized CommandHandler via SPI in sentinel-demo-command-handler as it's a demo module.

[all4you]

Maybe it's better to add an example to show how to register a customized CommandHandler via SPI in sentinel-demo-command-handler as it's a demo module.

done!

[sczyh30]

LGTM

[sczyh30]

Nice, thanks for contributing!