feat(gateway): add service-upstream annotation for delegated nginx

[michaelbeaumont]

Nginx seems to only support nginx.ingress.kubernetes.io/service-upstream. This proposes setting it unchecked but I suppose we could try to discover if the user is using nginx.

Checklist prior to review

• Link to docs PR or issue --
• Link to UI issue or PR --
• Is the issue worked on linked? --
• The PR does not hardcode values that might break projects that depend on kuma (e.g. "kumahq" as a image registry) --
• The PR will work for both Linux and Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Unit Tests --
• E2E Tests --
• Manual Universal Tests --
• Manual Kubernetes Tests --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? --
• Do you need to explicitly set a > Changelog: entry here?

[codecov-commenter]

Codecov Report

Merging #4913 (11f931e) into master (22c157d) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4913      +/-   ##
==========================================
+ Coverage   46.68%   46.70%   +0.01%     
==========================================
  Files         687      687              
  Lines       46656    46657       +1     
==========================================
+ Hits        21781    21790       +9     
+ Misses      22966    22960       -6     
+ Partials     1909     1907       -2     

Impacted Files	Coverage Δ
pkg/plugins/runtime/k8s/metadata/annotations.go	72.09% <ø> (ø)
...gins/runtime/k8s/controllers/service_controller.go	42.85% <100.00%> (+1.03%)	⬆️
pkg/core/resources/manager/cache.go	88.31% <0.00%> (+2.59%)	⬆️
pkg/plugins/leader/postgres/leader_elector.go	89.36% <0.00%> (+6.38%)	⬆️
pkg/xds/cache/once/cache.go	94.87% <0.00%> (+7.69%)	⬆️

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[lahabana]

I'm fine with with this the Nginx IC is so common that just adding the annotation regardless is fine to me.