Add traffic shifting strategy

[chenquanzhao]

What this PR does / why we need it:

For the sake of reducing downtime and risk of updating a service, we usually adopt Blue-Green Deployment or Gray Deployment that ensures the coexistence of the old and new service version. We can shift partial traffic to the new service by weight percentage or some extra routing rules, such as some keyword from cookie or request header and so on. And nginx ingress controller is served as the traffic entrypoint for all cluster services, it should offer the capability of traffic management.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #2419

Special notes for your reviewer:
Design doc: https://docs.google.com/document/d/1AkffGGtjy38n6GXRlTMPQpRUsto8zKjzCroZcJuXIs8/edit?usp=sharing
@aledbf

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[aledbf]

@chenqz1987 not sure about this because requires too many changes

[chenquanzhao]

@aledbf yeah... but it is a very valuable feature, and we can discuss the design and plan together. Do you have any idea or comments about the design?

[geun]

+1

[BSWANG]

+1

[k8s-ci-robot]

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[barockok]

+1

[dahsing]

+1

[codecov-io]

Codecov Report

Merging #2560 into master will decrease coverage by 1.81%.
The diff coverage is 23.39%.

@@            Coverage Diff             @@
##           master    #2560      +/-   ##
==========================================
- Coverage   40.77%   38.95%   -1.82%     
==========================================
  Files          74       76       +2     
  Lines        5077     5650     +573     
==========================================
+ Hits         2070     2201     +131     
- Misses       2724     3133     +409     
- Partials      283      316      +33

Impacted Files	Coverage Δ
internal/ingress/controller/config/config.go	98.23% <ø> (ø)	⬆️
internal/ingress/controller/controller.go	1.68% <0%> (-0.54%)	⬇️
internal/ingress/controller/nginx.go	11.45% <0%> (-0.06%)	⬇️
internal/ingress/annotations/annotations.go	81.25% <100%> (+0.6%)	⬆️
internal/ingress/types_equals.go	10.58% <3.75%> (-1.84%)	⬇️
internal/ingress/annotations/serviceweight/main.go	38.23% <38.23%> (ø)
internal/ingress/annotations/servicematch/main.go	40.35% <40.35%> (ø)
internal/ingress/controller/template/template.go	60.15% <48.63%> (-3.78%)	⬇️

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[aoxn]

+1

[cheyang]

+1

[yuyang0]

+1

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[ElvinEfendi]

@chenquanzhao thanks for this PR! I'd like to help to get this feature out as soon as possible. As @aledbf mentions above the PR introduces significant changes. I drafted a quick proposal that achieves approximately the same result with minimal changes only: https://docs.google.com/document/d/1qKTyLBLuKIYE6d6BsFXRM7zYB-2MUk6qJjtBL1KCz78/edit?usp=sharing

It would be great to get your opinions on it.

[chenquanzhao]

@ElvinEfendi Appreciate your help and I already add some comments to the document for your reference.

[yaron2]

Hi, any updates regarding this PR?

[ElvinEfendi]

@yaron2 the feature is being implemented at Shopify#120. Most likely it will land in dev build of master branch by the end of this week.