Add omitempty flag to stage config

[OlivierCazade]

We recently started using the config API in the NOO to configure FLP.

Some attributes do not have the omitempty flag resulting in them getting converted in json with an empty string or 0 as value instead of using the internal default value of FLP.

[codecov-commenter]

Codecov Report

Merging #229 (18be06a) into main (217223d) will increase coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #229      +/-   ##
==========================================
+ Coverage   61.53%   61.71%   +0.17%     
==========================================
  Files          67       67              
  Lines        3897     3897              
==========================================
+ Hits         2398     2405       +7     
+ Misses       1352     1346       -6     
+ Partials      147      146       -1     

Flag	Coverage Δ
unittests	61.71% <ø> (+0.17%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/api/conn_track.go	100.00% <ø> (ø)
pkg/api/encode_kafka.go	100.00% <ø> (ø)
pkg/api/encode_prom.go	100.00% <ø> (ø)
pkg/api/transform_filter.go	100.00% <ø> (ø)
pkg/api/transform_generic.go	0.00% <ø> (ø)
pkg/api/transform_network.go	100.00% <ø> (ø)
pkg/pipeline/utils/exit.go	100.00% <0.00%> (+41.17%)	⬆️

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[jotak]

lgtm