server: Rate limiter and audit

[CabinfeverB]

What problem does this PR solve?

This is a child PR of #4466
For details, please refer to #4466

NOTE: This PR will not merge.

What is changed and how it works?

implement ApiRateLimiter and AuditLogger

Check List

Tests

• No code

Release note

None

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[codecov]

Codecov Report

Merging #4470 (e7ae2bf) into master (e7c795f) will decrease coverage by 0.21%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #4470      +/-   ##
==========================================
- Coverage   74.96%   74.74%   -0.22%     
==========================================
  Files         264      264              
  Lines       27796    27825      +29     
==========================================
- Hits        20837    20798      -39     
- Misses       5115     5170      +55     
- Partials     1844     1857      +13     

Flag	Coverage Δ
unittests	74.74% <0.00%> (-0.22%)	⬇️

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

Impacted Files	Coverage Δ
pkg/apiutil/apiutil.go	36.61% <0.00%> (-25.29%)	⬇️
server/kv/etcd_kv.go	69.56% <0.00%> (-10.15%)	⬇️
server/tso/local_allocator.go	64.86% <0.00%> (-6.76%)	⬇️
server/tso/tso.go	61.36% <0.00%> (-5.12%)	⬇️
server/schedulers/random_merge.go	60.00% <0.00%> (-3.34%)	⬇️
server/tso/allocator_manager.go	64.83% <0.00%> (-2.84%)	⬇️
server/election/leadership.go	75.25% <0.00%> (-2.07%)	⬇️
server/core/hot_region_storage.go	77.33% <0.00%> (-1.34%)	⬇️
pkg/btree/btree.go	85.78% <0.00%> (-0.97%)	⬇️
server/encryptionkm/key_manager.go	72.90% <0.00%> (-0.80%)	⬇️
... and 9 more

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[CabinfeverB]

close this PR to change spliting small PRs