Enable configuration of plugins using configmap

[aledbf]

What this PR does / why we need it:

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Which issue/s this PR fixes

fixes #5196

How Has This Been Tested?

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added tests to cover my changes.
• All new and existing tests passed.

[aledbf]

/retest

[codecov-io]

Codecov Report

Merging #5331 into master will decrease coverage by 0.07%.
The diff coverage is 61.90%.

@@            Coverage Diff             @@
##           master    #5331      +/-   ##
==========================================
- Coverage   58.70%   58.62%   -0.08%     
==========================================
  Files          88       88              
  Lines        6908     6914       +6     
==========================================
- Hits         4055     4053       -2     
- Misses       2410     2416       +6     
- Partials      443      445       +2     

Impacted Files	Coverage Δ
cmd/nginx/flags.go	82.38% <ø> (-0.71%)	⬇️
internal/ingress/controller/template/configmap.go	75.58% <0.00%> (-1.82%)	⬇️
internal/ingress/controller/store/store.go	60.08% <66.66%> (+0.12%)	⬆️
internal/ingress/controller/controller.go	49.40% <100.00%> (ø)
internal/ingress/controller/template/template.go	80.10% <100.00%> (ø)

---

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[ElvinEfendi]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [ElvinEfendi,aledbf]

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