labeler: add index to support rule override

[disksing]

Signed-off-by: disksing i@disksing.com

What problem does this PR solve?

Fix #4031

What is changed and how it works?

Add Index field to RegionLabelRule. When multiple rules defines label with the same key, only the one with the maximum index takes effect. When there are multiple rules have an index equal to maximum value, the returned value is undefined behavior.

Check List

Tests

• Unit test

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JmPotato
• rleungx

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[codecov]

Codecov Report

Merging #4032 (704d338) into master (692e003) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4032      +/-   ##
==========================================
- Coverage   74.58%   74.54%   -0.04%     
==========================================
  Files         256      256              
  Lines       25866    25877      +11     
==========================================
- Hits        19293    19291       -2     
- Misses       4859     4869      +10     
- Partials     1714     1717       +3     

Flag	Coverage Δ
unittests	74.54% <100.00%> (-0.04%)	⬇️

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

Impacted Files	Coverage Δ
server/schedule/labeler/labeler.go	79.41% <100.00%> (+1.81%)	⬆️
server/kv/etcd_kv.go	72.46% <0.00%> (-7.25%)	⬇️
server/schedule/operator/step.go	67.44% <0.00%> (-2.33%)	⬇️
server/server.go	70.51% <0.00%> (-1.07%)	⬇️
server/cluster/coordinator.go	72.07% <0.00%> (-0.91%)	⬇️
server/schedule/operator_controller.go	84.75% <0.00%> (-0.80%)	⬇️
server/cluster/cluster.go	82.22% <0.00%> (-0.36%)	⬇️
server/tso/tso.go	65.19% <0.00%> (ø)
server/grpc_service.go	47.45% <0.00%> (+0.22%)	⬆️
server/member/member.go	65.24% <0.00%> (+0.53%)	⬆️
... and 3 more

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[JmPotato]

/merge

[ti-chi-bot]

@JmPotato: 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: 704d338