[DNM]: tolerate a single TiKV outage

[BornChanger]

What problem does this PR solve?

What is changed and how does it work?

Code changes

• [ ] Has Go code change
• [ ] Has CI related scripts change

Tests

• [ ] Unit test
• [ ] E2E test
• [ ] Manual test
• [ ] No code

Side effects

• [ ] Breaking backward compatibility
• [ ] Other side effects:

Related changes

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

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Once this PR has been reviewed and has the lgtm label, please ask for approval from bornchanger, ensuring that each of them provides their approval before proceeding. For more information see the Code Review Process.

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Needs approval from an approver in each of these files: - **[OWNERS](https://github.com/pingcap/tidb-operator/blob/release-1.5/OWNERS)** Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 61.58%. Comparing base (a1425dc) to head (e169cea).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release-1.5 #5579 +/- ## ============================================ Coverage 61.58% 61.58% ============================================ Files 229 229 Lines 29300 29301 +1 ============================================ + Hits 18045 18046 +1 Misses 9478 9478 Partials 1777 1777 ``` | [Flag](https://app.codecov.io/gh/pingcap/tidb-operator/pull/5579/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | Coverage Δ | | |---|---|---| | [unittest](https://app.codecov.io/gh/pingcap/tidb-operator/pull/5579/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `61.58% <33.33%> (+<0.01%)` | :arrow_up: |

[ti-chi-bot[bot]]

PR needs rebase.

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