Add balance leader score option for release 3.0

[lhy1024]

Signed-off-by: lhy1024 admin@liudos.us

What problem does this PR solve?

• cherry pick from scheduler: change balance leader score #1743
• set default strategy to 'bySize'
• cherry pick from config: rename LeaderScheduleStrategy to LeaderSchedulePolicy #2075

Check List

Tests

• Unit test

Release note

Add balance leader score option, It will be allowed to count leader score according to size or count.

[lhy1024]

/run-all-tests

[lhy1024]

/run-all-tests

[codecov-commenter]

Codecov Report

Merging #2479 into release-3.0 will decrease coverage by 0.05%.
The diff coverage is 92.85%.

@@               Coverage Diff               @@
##           release-3.0    #2479      +/-   ##
===============================================
- Coverage        69.92%   69.86%   -0.06%     
===============================================
  Files              171      171              
  Lines            16896    16983      +87     
===============================================
+ Hits             11814    11866      +52     
- Misses            4120     4145      +25     
- Partials           962      972      +10     

Impacted Files	Coverage Δ
server/core/resource_kind.go	78.57% <80.00%> (+3.57%)	⬆️
server/core/store.go	76.17% <81.81%> (-0.22%)	⬇️
server/schedulers/balance_region.go	89.51% <83.33%> (+5.14%)	⬆️
server/schedule/operator_controller.go	87.03% <84.61%> (-0.16%)	⬇️
pkg/mock/mockcluster/mockcluster.go	90.68% <100.00%> (+0.17%)	⬆️
pkg/mock/mockoption/mockoption.go	92.77% <100.00%> (+0.27%)	⬆️
server/api/store.go	54.88% <100.00%> (ø)
server/cluster_info.go	88.38% <100.00%> (+0.04%)	⬆️
server/config.go	83.37% <100.00%> (+0.22%)	⬆️
server/core/test_util.go	94.73% <100.00%> (+1.87%)	⬆️
... and 16 more

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[lhy1024]

/run-integration-common-test

[lhy1024]

/run-all-tests

[lhy1024]

/run-test

[lhy1024]

/run-all-tests

[rleungx]

/merge

[sre-bot]

/run-all-tests