mcs: register tso allocator

[rleungx]

What problem does this PR solve?

Issue Number: Close #xxx

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 the 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

None.

[ti-chi-bot]

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[codecov]

Codecov Report

Attention: Patch coverage is 89.58333% with 10 lines in your changes missing coverage. Please review.

Project coverage is 77.39%. Comparing base (340c58c) to head (7f23d25).
Report is 203 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7891      +/-   ##
==========================================
+ Coverage   77.36%   77.39%   +0.02%     
==========================================
  Files         468      468              
  Lines       60943    61035      +92     
==========================================
+ Hits        47146    47235      +89     
+ Misses      10252    10245       -7     
- Partials     3545     3555      +10     

Flag	Coverage Δ
unittests	77.39% <89.58%> (+0.02%)	⬆️

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

[JmPotato]

What about setting a const for 3?

[JmPotato]

The allocatorKeyPrefix varies in different modes, and it cannot retrieve keys from other allocators as expected.

[rleungx]

nice catch!

[ti-chi-bot]

[FORMAT CHECKER NOTIFICATION]

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[ti-chi-bot]

PR needs rebase.

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