Add support for session affinity during weighted routing with Istio

[aryan9600]

Add support for session affinity/sticky sessions during weighted routing with Istio, i.e. when a user is routed to the canary deployment, all subsequent requests from that user will hit the canary deployments, even though weighted routing is active.

This feature can be enabled by specifying a .spec.analysis.sessionAffinty.cookieName. This value combined with a random sequence (<cookie-name>: <random-sequence>) is used as the value of the Set-Cookie header, and then all requests' headers that match against this value are sent to the canary deployment. Users can also specify .spec.analysis.sessionAffinity.maxAge to configure the lifetime of the cookie being set.

Fixes: #1198, #1232

[codecov-commenter]

Codecov Report

Base: 54.45% // Head: 54.72% // Increases project coverage by +0.27% 🎉

Coverage data is based on head (b095713) compared to base (882286d).
Patch coverage: 82.17% of modified lines in pull request are covered.

❗ Current head b095713 differs from pull request most recent head d16c969. Consider uploading reports for the commit d16c969 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1280      +/-   ##
==========================================
+ Coverage   54.45%   54.72%   +0.27%     
==========================================
  Files          81       81              
  Lines        9408     9515     +107     
==========================================
+ Hits         5123     5207      +84     
- Misses       3663     3682      +19     
- Partials      622      626       +4     

Impacted Files	Coverage Δ
pkg/router/istio.go	76.89% <82.17%> (+0.45%)	⬆️

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[stefanprodan]

Please document this feature in deployment-strategies.md and in the Istio guides.

[stefanprodan]

LGTM

Thanks @aryan9600 🏅