Fix the compatibility with PD v3.x

[lucklove]

What problem does this PR solve?

In #1161, we introduce a mechanism which temporarily increase schedule limit during upgrading/reloading tikv, to speed up the upgrade process. But the v3.x of PD doesn't support config schedule limit at all:

What is changed and how it works?

Check the current version of PD, only apply the mechanism on v4.x or latter.

Check List

Tests

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

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

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

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release notes:

NONE

[codecov-io]

Codecov Report

Merging #1274 (48b3a37) into master (cf55cab) will increase coverage by 0.27%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1274      +/-   ##
==========================================
+ Coverage   26.23%   26.50%   +0.27%     
==========================================
  Files         263      275      +12     
  Lines       18884    19322     +438     
==========================================
+ Hits         4954     5122     +168     
- Misses      13158    13412     +254     
- Partials      772      788      +16     

Flag	Coverage Δ
integrate	16.04% <0.00%> (-0.50%)	⬇️
playground	3.10% <0.00%> (?)
tiup	16.52% <0.00%> (-0.03%)	⬇️
unittest	22.73% <0.00%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
pkg/cluster/api/pdapi.go	0.00% <0.00%> (ø)
components/playground/instance/tiflash.go	0.00% <0.00%> (ø)
components/playground/instance/process.go	0.00% <0.00%> (ø)
...onents/playground/instance/tiflash_proxy_config.go	0.00% <0.00%> (ø)
components/playground/instance/instance.go	0.00% <0.00%> (ø)
components/playground/instance/ticdc.go	0.00% <0.00%> (ø)
components/playground/instance/tiflash_config.go	0.00% <0.00%> (ø)
components/playground/instance/tidb.go	0.00% <0.00%> (ø)
components/playground/instance/drainer.go	0.00% <0.00%> (ø)
components/playground/instance/pump.go	0.00% <0.00%> (ø)
... and 7 more

---

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• AstroProfundis

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[AstroProfundis]

/merge

[ti-chi-bot]

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

Commit hash: ffb209c