mvcc/kvstore: Optimize compaction, slove conflict for #11150

[shenjiangc]

mvcc/kvstore: Optimize compaction

when the number of key-value index is greater than one million, compact take too long and blocks other requests.
Move the “kvindex.Compact” to “fifoSched.Schedule” func

slove conflict for #11150

[codecov-io]

Codecov Report

Merging #11330 into master will increase coverage by 0.2%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #11330     +/-   ##
=========================================
+ Coverage   64.05%   64.26%   +0.2%     
=========================================
  Files         403      403             
  Lines       37970    37969      -1     
=========================================
+ Hits        24323    24400     +77     
+ Misses      12011    11940     -71     
+ Partials     1636     1629      -7

Impacted Files	Coverage Δ
mvcc/kvstore.go	86.05% <100%> (-0.05%)	⬇️
auth/simple_token.go	68.29% <0%> (-18.7%)	⬇️
clientv3/namespace/watch.go	87.87% <0%> (-6.07%)	⬇️
proxy/grpcproxy/watcher.go	89.79% <0%> (-4.09%)	⬇️
pkg/testutil/recorder.go	77.77% <0%> (-3.71%)	⬇️
clientv3/leasing/cache.go	88.88% <0%> (-2.78%)	⬇️
clientv3/concurrency/election.go	79.68% <0%> (-2.35%)	⬇️
proxy/grpcproxy/watch.go	88.75% <0%> (-1.19%)	⬇️
clientv3/leasing/kv.go	89.7% <0%> (-1%)	⬇️
etcdserver/server.go	68.67% <0%> (+0.19%)	⬆️
... and 19 more

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[jingyih]

Code change looks good to me. Could you please clean up the commits?

[WIZARD-CXY]

LGTM

[jingyih]

LGTM

[jingyih]

Test failure unrelated.