mcs: add a switch to dynamically enable scheduling service

[rleungx]

What problem does this PR solve?

Issue Number: Ref #5839.

What is changed and how does it work?

This PR adds a switch to dynamically enable scheduling service. If we only upgrade the scheduling service, the logic could be different from the logic inside the api service. To avoid the changes of different logic bringing some troubles, we use a config to let the users control it by themselves.

Check List

Tests

• Unit test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• CabinfeverB
• nolouch

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[codecov]

Codecov Report

Merging #7595 (cb367e7) into master (6472313) will increase coverage by 0.01%.
The diff coverage is 51.42%.

❗ Current head cb367e7 differs from pull request most recent head ee9014b. Consider uploading reports for the commit ee9014b to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7595      +/-   ##
==========================================
+ Coverage   73.72%   73.73%   +0.01%     
==========================================
  Files         429      429              
  Lines       47498    47503       +5     
==========================================
+ Hits        35018    35027       +9     
+ Misses       9498     9486      -12     
- Partials     2982     2990       +8     

Flag	Coverage Δ
unittests	73.73% <51.42%> (+0.01%)	⬆️

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[CabinfeverB]

LGTM. But I think there's a little bit of learning cost to using this configuration

[CabinfeverB]

I test it by pd-ctl

Before

config set enable-dynamic-switch "false"

After

[rleungx]

change to enable-scheduling-fallback

[rleungx]

/merge

[ti-chi-bot]

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/run-all-tests

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[ti-chi-bot]

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

Commit hash: cb367e7

[ti-chi-bot]

@rleungx: Your PR was out of date, I have automatically updated it for you.

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