*: decouple coordinator with server

[rleungx]

What problem does this PR solve?

Issue Number: Ref #5839.

What is changed and how does it work?

Part of #6418.

Check List

Tests

• Unit test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• binshi-bing
• nolouch

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[codecov]

Codecov Report

Patch coverage: 84.03% and project coverage change: +0.04 🎉

Comparison is base (bf7edf5) 74.97% compared to head (cca1adc) 75.01%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6503      +/-   ##
==========================================
+ Coverage   74.97%   75.01%   +0.04%     
==========================================
  Files         410      411       +1     
  Lines       41996    42029      +33     
==========================================
+ Hits        31487    31529      +42     
+ Misses       7753     7746       -7     
+ Partials     2756     2754       -2     

Flag	Coverage Δ
unittests	75.01% <84.03%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/schedule/checker/checker_controller.go	80.00% <ø> (ø)
pkg/schedule/config/config.go	33.33% <ø> (ø)
pkg/schedule/operator/operator_controller.go	86.54% <ø> (ø)
server/api/plugin.go	8.57% <0.00%> (ø)
server/cluster/metrics.go	100.00% <ø> (ø)
server/handler.go	52.78% <0.00%> (ø)
tools/pd-ctl/pdctl/command/plugin_command.go	41.02% <0.00%> (ø)
pkg/schedule/diagnostic_manager.go	75.26% <50.00%> (ø)
pkg/mock/mockcluster/mockcluster.go	93.04% <67.85%> (-1.51%)	⬇️
pkg/schedule/coordinator.go	73.33% <86.36%> (ø)
... and 13 more

... and 36 files with indirect coverage changes

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[binshi-bing]

The reset looks good to me

[nolouch]

lgtm

[JmPotato]

/merge

[ti-chi-bot]

@JmPotato: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: d7ae9d7