rule_checker: can replace unhealthPeer with orphanPeer (#6831)

[ti-chi-bot]

This is an automated cherry-pick of #6831

What problem does this PR solve?

Issue Number: Close #6559

When Region looks like the below, and there were only 4 stores:

{
  "id": 55929554,
  "start_key": "748000000000000BFF065F728000000042FFEF8B7A0000000000FA",
  "end_key": "748000000000000BFF065F728000000042FFF07AFD0000000000FA",
  "epoch": {
    "conf_ver": 6,
    "version": 109399
  },
  "peers": [
    {
      "id": 55929555,
      "store_id": 1,
      "role_name": "Voter"
    },
    {
      "id": 55929556,
      "store_id": 4,
      "role_name": "Voter"
    },
    {
      "id": 55929557,
      "store_id": 5,
      "role_name": "Voter"
    },
    {
      "id": 55929558,
      "store_id": 2751139,
      "role": 1,
      "role_name": "Learner",
      "is_learner": true
    }
  ],
  "leader": {
    "id": 55929555,
    "store_id": 1,
    "role_name": "Voter"
  },
  "down_peers": [
    {
      "down_seconds": 40307,
      "peer": {
        "id": 55929556,
        "store_id": 4,
        "role_name": "Voter"
      }
    }
  ],
  "pending_peers": [
    {
      "id": 55929556,
      "store_id": 4,
      "role_name": "Voter"
    }
  ],
  "cpu_usage": 0,
  "written_bytes": 0,
  "read_bytes": 0,
  "written_keys": 0,
  "read_keys": 0,
  "approximate_size": 1,
  "approximate_keys": 40960
}

and the region fit likes:

{
  "rule-fits": [
    {
      "rule": {
        "group_id": "pd",
        "id": "default",
        "start_key": "",
        "end_key": "",
        "role": "voter",
        "is_witness": false,
        "count": 3,
        "location_labels": [
          "region",
          "zone",
          "host"
        ]
      },
      "peers": [
        {
          "id": 55929555,
          "store_id": 1
        },
        {
          "id": 55929557,
          "store_id": 5
        },
        {
          "id": 55929556,
          "store_id": 4
        }
      ],
      "peers-different-role": null,
      "isolation-score": 300
    }
  ],
  "orphan-peers": [
    {
      "id": 55929558,
      "store_id": 2751139,
      "role": 1
    }
  ]
}

cannot fix the region, always report as an unhealthy region. and store 4 is gone.

What is changed and how does it work?

add logic try to replace unhealthy peer with orphan peer

Check List

Tests

• Unit test

Release note

None.

[ti-chi-bot]

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• nolouch
• rleungx

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[codecov]

Codecov Report

Patch coverage: 75.00% and project coverage change: +0.09% 🎉

Comparison is base (bd94a98) 75.61% compared to head (18dc32d) 75.70%.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-6.5    #6843      +/-   ##
===============================================
+ Coverage        75.61%   75.70%   +0.09%     
===============================================
  Files              328      328              
  Lines            33128    33168      +40     
===============================================
+ Hits             25050    25111      +61     
+ Misses            5921     5912       -9     
+ Partials          2157     2145      -12     

Flag	Coverage Δ
unittests	75.70% <75.00%> (+0.09%)	⬆️

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

Files Changed	Coverage Δ
server/schedule/placement/fit.go	97.14% <0.00%> (-1.13%)	⬇️
server/schedule/operator/create_operator.go	90.85% <72.72%> (-0.71%)	⬇️
server/schedule/checker/rule_checker.go	82.78% <76.92%> (-0.68%)	⬇️
server/schedule/operator/builder.go	86.52% <100.00%> (+0.08%)	⬆️
server/schedule/operator/operator.go	92.51% <100.00%> (ø)

... and 29 files with indirect coverage changes

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[nolouch]

/merge

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[ti-chi-bot]

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

Commit hash: 18dc32d