statistics: pd can calculate the hot degree of the buckets.

[bufferflies]

What problem does this PR solve?

Issue Number: Close #4726

What is changed and how it works?

using btree to store the map relation betweeen the key range and buckekItem.
using map to store the map relation between the region-id and bucketItem.

every bucket has own hotgree and inherits the highest degree of the overlaps.
suck like this:

origin buckets
|--10--|--20--|--30--|--40--|
|--2--|--3--|--4--|--5--|

after inheriting
|--10-|--30--|--35--|
|--3-|--3--|--4--|

Check List

Tests

• Unit test
• Integration test

Code changes

Side effects

Related changes

Release note

pd can calculate the hot degree of the buckets.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• HunDunDM
• nolouch

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[codecov]

Codecov Report

Merging #4727 (d68802f) into master (563a93d) will decrease coverage by 0.07%.
The diff coverage is 84.53%.

@@            Coverage Diff             @@
##           master    #4727      +/-   ##
==========================================
- Coverage   75.43%   75.36%   -0.08%     
==========================================
  Files         303      306       +3     
  Lines       30015    30194     +179     
==========================================
+ Hits        22643    22756     +113     
- Misses       5386     5436      +50     
- Partials     1986     2002      +16     

Flag	Coverage Δ
unittests	75.36% <84.53%> (-0.08%)	⬇️

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

Impacted Files	Coverage Δ
server/cluster/cluster_worker.go	68.96% <50.00%> (-0.95%)	⬇️
server/statistics/buckets/hot_bucket_task.go	50.00% <50.00%> (ø)
server/statistics/buckets/hot_bucket_cache.go	82.41% <82.41%> (ø)
server/statistics/buckets/bucket_stat_informer.go	91.17% <91.17%> (ø)
pkg/keyutil/util.go	100.00% <100.00%> (ø)
pkg/rangetree/range_tree.go	98.30% <100.00%> (+0.05%)	⬆️
server/cluster/cluster.go	83.02% <100.00%> (+0.39%)	⬆️
pkg/metricutil/metricutil.go	82.75% <0.00%> (-10.35%)	⬇️
server/tso/local_allocator.go	64.86% <0.00%> (-6.76%)	⬇️
server/tso/tso.go	68.92% <0.00%> (-5.65%)	⬇️
... and 11 more

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[nolouch]

lgtm

[bufferflies]

/merge

[ti-chi-bot]

@bufferflies: 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: d68802f