resource_manager: the implement of server

[nolouch]

What problem does this PR solve?

Issue Number: Close #4399

What is changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

Please add a release note.

Please refer to [Release Notes Language Style Guide](https://pingcap.github.io/tidb-dev-guide/contribute-to-tidb/release-notes-style-guide.html) to write a quality release note.

If you don't think this PR needs a release note then fill it with None.

[ti-chi-bot]

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[codecov]

Codecov Report

Base: 75.57% // Head: 75.52% // Decreases project coverage by -0.05% ⚠️

Coverage data is based on head (3ab96a1) compared to base (8227cdb).
Patch coverage: 76.92% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5761      +/-   ##
==========================================
- Coverage   75.57%   75.52%   -0.06%     
==========================================
  Files         329      331       +2     
  Lines       32965    32984      +19     
==========================================
- Hits        24914    24911       -3     
- Misses       5902     5920      +18     
- Partials     2149     2153       +4     

Flag	Coverage Δ
unittests	75.52% <76.92%> (-0.06%)	⬇️

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

Impacted Files	Coverage Δ
server/storage/endpoint/key_path.go	90.90% <0.00%> (-2.12%)	⬇️
server/storage/endpoint/resource_group.go	0.00% <0.00%> (ø)
server/storage/storage.go	67.30% <ø> (-3.85%)	⬇️
pkg/mcs/resource_manager/client/client.go	75.00% <75.00%> (ø)
server/server.go	74.87% <88.88%> (-1.02%)	⬇️
pkg/dashboard/adapter/manager.go	74.71% <0.00%> (-4.60%)	⬇️
server/region_syncer/server.go	82.96% <0.00%> (-4.40%)	⬇️
pkg/utils/etcdutil/etcdutil.go	84.88% <0.00%> (-3.49%)	⬇️
server/schedulers/shuffle_hot_region.go	55.12% <0.00%> (-2.57%)	⬇️
... and 35 more

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[ti-chi-bot]

@nolouch: PR needs rebase.

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