chore(pd): refactor and fix pd tests

[VGalaxies]

subtask of #2481

---

1. remove pd-clitools module (replace with pd-cli when adapting 4.0)
2. fix code style
3. remove useless test classes, such as DiscoveryClientImplTest, although DiscoveryClientImpl is still retained in pd-client
4. all core tests inherit from PDCoreTestBase to reuse the PDConfig construction

For detailed documentation, please refer to this link.

[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 6 lines in your changes are missing coverage. Please review.

❗ No coverage uploaded for pull request base (pd-store@6d04e9b). Click here to learn what that means.

Files	Patch %	Lines
...va/org/apache/hugegraph/pd/client/ClientCache.java	14.28%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             pd-store    #2492   +/-   ##
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  Coverage            ?   56.82%           
  Complexity          ?     2156           
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  Files               ?      717           
  Lines               ?    58318           
  Branches            ?     7482           
===========================================
  Hits                ?    33140           
  Misses              ?    21943           
  Partials            ?     3235           

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[imbajin]

The relative doc & previous issues help me a lot :)

Miss some context before reading them