A/B testing support for Gloo Edge ingress controller

[kdorosh]

Resolves #707 , which is related to solo-io/gloo#3726

The approach here is to replace Gloo UpstreamGroups in the flagger implementation with Gloo RouteTables, which additionally support header/method matching used in A/B testing. For this to work, we needed to add and leverage the new inheritablePathMatcher field on Gloo RouteTables, thus these changes will only work in Gloo Edge 1.6.0-beta22 and higher. (Gloo Edge 1.6.0 release is slated for end of year)

Unit and integration tests all pass locally. The documented guide has been updated and confirmed as well.

Appreciate the attention to developer experience and developer guide, thanks!

[codecov-io]

Codecov Report

Merging #765 (005e392) into main (cff742d) will increase coverage by 0.44%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##             main     #765      +/-   ##
==========================================
+ Coverage   56.02%   56.47%   +0.44%     
==========================================
  Files          67       67              
  Lines        5340     5383      +43     
==========================================
+ Hits         2992     3040      +48     
+ Misses       1891     1882       -9     
- Partials      457      461       +4     

Impacted Files	Coverage Δ
pkg/router/gloo.go	81.63% <83.33%> (+12.40%)	⬆️

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[stefanprodan]

LGTM

Thanks @kdorosh 🏅