config: fix the store limit cannot be persisted (#3380)

[ti-srebot]

cherry-pick #3380 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In pd repo:
git pr https://github.com/tikv/pd/pull/3403

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/pd.git pr/3403:release-4.0-028befdbe8e0

---

What problem does this PR solve?

The store limit cannot persist due to we only change the value in the memory. Close #3382.

What is changed and how it works?

This PR persists the store limit once it changes and if persistence fails, we will roll back to the original one.

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

• Fix the issue that the store limit cannot be persisted

[ti-chi-bot]

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[ti-srebot]

@rleungx you're already a collaborator in bot's repo.

[nolouch]

lgtm

[rleungx]

/run-all-tests

[HunDunDM]

/merge

[ti-chi-bot]

@HunDunDM: 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: ffe37dc

[rleungx]

/run-unit-tests

[codecov]

Codecov Report

Merging #3403 (ffe37dc) into release-4.0 (28269fc) will decrease coverage by 0.13%.
The diff coverage is 56.75%.

@@               Coverage Diff               @@
##           release-4.0    #3403      +/-   ##
===============================================
- Coverage        74.75%   74.62%   -0.14%     
===============================================
  Files              209      209              
  Lines            19760    19789      +29     
===============================================
- Hits             14772    14767       -5     
- Misses            3653     3681      +28     
- Partials          1335     1341       +6     

Flag	Coverage Δ
unittests	74.62% <56.75%> (-0.14%)	⬇️

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

Impacted Files	Coverage Δ
server/cluster/store_limiter.go	51.06% <ø> (ø)
server/config/persist_options.go	87.16% <50.00%> (ø)
server/cluster/cluster.go	78.05% <54.83%> (-0.92%)	⬇️
server/handler.go	44.00% <66.66%> (-0.28%)	⬇️
pkg/mock/mockoption/mockoption.go	90.32% <100.00%> (+0.10%)	⬆️
pkg/errs/errs.go	75.00% <0.00%> (-25.00%)	⬇️
server/kv/etcd_kv.go	69.56% <0.00%> (-10.15%)	⬇️
server/member/leader.go	63.76% <0.00%> (-5.05%)	⬇️
server/id/id.go	76.19% <0.00%> (-4.77%)	⬇️
pkg/dashboard/adapter/manager.go	84.78% <0.00%> (-4.35%)	⬇️
... and 8 more

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