placement: use id as store key (#2205)

[disksing]

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

What problem does this PR solve?

cherry-pick #2205 to resolve #2203

What is changed and how it works?

• startKey and endKey can be duplicated, use groupID+ID instead
• check data consistency and recover when load rules

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)
  • insert some rules with same key, make sure it won't be over written
  • use old pd to write some rules, then start new pd, the wrong key are recovered

Code changes

• Has persistent data change

[codecov-io]

Codecov Report

Merging #2222 into release-3.1 will decrease coverage by 0.06%.
The diff coverage is 41.46%.

@@               Coverage Diff               @@
##           release-3.1    #2222      +/-   ##
===============================================
- Coverage        74.87%   74.81%   -0.07%     
===============================================
  Files              195      195              
  Lines            19987    20006      +19     
===============================================
+ Hits             14965    14967       +2     
- Misses            3884     3894      +10     
- Partials          1138     1145       +7

Impacted Files	Coverage Δ
server/schedule/placement/rule.go	94.11% <100%> (ø)	⬆️
server/core/storage.go	72.72% <100%> (+0.86%)	⬆️
server/schedule/placement/rule_manager.go	71.12% <31.42%> (-11.67%)	⬇️
server/tso/tso.go	77.37% <0%> (-5.11%)	⬇️
server/region_syncer/client.go	78.44% <0%> (-2.59%)	⬇️
pkg/etcdutil/etcdutil.go	82.6% <0%> (-1.45%)	⬇️
server/member/leader.go	75.51% <0%> (-1.03%)	⬇️
pkg/btree/btree.go	86.84% <0%> (-0.81%)	⬇️
server/server.go	63.89% <0%> (-0.43%)	⬇️
server/handler.go	51.61% <0%> (+0.43%)	⬆️
... and 3 more

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[disksing]

/merge

[sre-bot]

/run-all-tests

[sre-bot]

@disksing merge failed.

[disksing]

/merge

[sre-bot]

/run-all-tests

[sre-bot]

@disksing merge failed.

[disksing]

/merge

[sre-bot]

/run-all-tests

[sre-bot]

@disksing merge failed.

[disksing]

/run-integration-common-test tidb-test=release-3.1

[disksing]

/merge

[sre-bot]

/run-all-tests