Add support for grpc_set_header

[aledbf]

Which issue this PR fixes:

fixes #2493
fixes #2407

[aledbf]

adding tests :)

[antoineco]

Needs rebase on #2528.

[aledbf]

Needs rebase

done

[codecov-io]

Codecov Report

Merging #2524 into master will increase coverage by 0.01%.
The diff coverage is 37.5%.

@@            Coverage Diff             @@
##           master    #2524      +/-   ##
==========================================
+ Coverage   40.73%   40.74%   +0.01%     
==========================================
  Files          73       73              
  Lines        5015     5021       +6     
==========================================
+ Hits         2043     2046       +3     
- Misses       2700     2701       +1     
- Partials      272      274       +2

Impacted Files	Coverage Δ
internal/ingress/controller/controller.go	2.25% <ø> (ø)	⬆️
internal/ingress/controller/template/template.go	64.97% <37.5%> (-0.48%)	⬇️

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[antoineco]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, antoineco

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