General Design for Metrics(memory、cpu...) adaptive flow control

[liqiangz]

Describe what this PR does / why we need it

General Design for Metrics(memory、cpu...) adaptive flow control

Does this pull request fix one issue?

Fixes #368

Describe how you did it

Refer to #368

Describe how to verify it

Special notes for reviews

[codecov-io]

Codecov Report

Merging #387 (cd40568) into master (588100c) will decrease coverage by 1.87%. The diff coverage is 51.09%.

@@            Coverage Diff             @@
##           master     #387      +/-   ##
==========================================
- Coverage   52.43%   50.56%   -1.88%     
==========================================
  Files          69       78       +9     
  Lines        4226     4703     +477     
==========================================
+ Hits         2216     2378     +162     
- Misses       1692     1983     +291     
- Partials      318      342      +24     

Impacted Files	Coverage Δ
core/flow/rule_manager.go	62.34% <0.00%> (+1.89%)	:arrow_up:
core/adaptive/config.go	14.28% <14.28%> (ø)
core/flow/rule.go	26.66% <33.33%> (-0.79%)	:arrow_down:
core/flow/tc_default.go	60.86% <50.00%> (-3.84%)	:arrow_down:
core/adaptive/adaptive_manager.go	55.84% <55.84%> (ø)
core/adaptive/controller.go	86.95% <86.95%> (ø)
pkg/datasource/nacos/nacos.go	58.00% <0.00%> (ø)
pkg/datasource/consul/consul.go	32.14% <0.00%> (ø)
pkg/datasource/k8s/k8s.go	1.78% <0.00%> (ø)
... and 6 more

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