fix wrong json tag

[oilbeater]

What this PR does / why we need it:
json tags are case sensitive when encoding, change omitEmpty to omitempty

[codecov-io]

Codecov Report

Merging #2193 into master will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #2193      +/-   ##
=========================================
+ Coverage   36.54%   36.6%   +0.06%     
=========================================
  Files          70      70              
  Lines        4884    4884              
=========================================
+ Hits         1785    1788       +3     
+ Misses       2822    2820       -2     
+ Partials      277     276       -1

Impacted Files	Coverage Δ
internal/ingress/annotations/authreq/main.go	54.79% <ø> (ø)	⬆️
internal/ingress/annotations/ipwhitelist/main.go	44.44% <ø> (ø)	⬆️
cmd/nginx/main.go	23.44% <0%> (+2.06%)	⬆️

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[aledbf]

/approve

[aledbf]

@oilbeater thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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