show approximate_kv_size in pd-ctl

[zeminzhou]

What problem does this PR solve?

Issue Number: Close #8412

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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.32%. Comparing base (0b5ed0f) to head (a455951).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8403      +/-   ##
==========================================
+ Coverage   77.21%   77.32%   +0.11%     
==========================================
  Files         471      471              
  Lines       61806    61835      +29     
==========================================
+ Hits        47723    47815      +92     
+ Misses      10491    10420      -71     
- Partials     3592     3600       +8     

Flag	Coverage Δ
unittests	77.32% <100.00%> (+0.11%)	⬆️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nolouch, rleungx

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Needs approval from an approver in each of these files:

• OWNERS [nolouch,rleungx]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-07-17 05:06:34.463726774 +0000 UTC m=+416816.454668244: ☑️ agreed by nolouch.
• 2024-07-17 05:49:46.459204204 +0000 UTC m=+419408.450145675: ☑️ agreed by rleungx.