made encode a terminal stage

[KalmanMeth]

Made encode_prom (and other encode stages) into a terminal stage.
We then do not need to add write_none as a dummy terminal stage.

[codecov-commenter]

Codecov Report

Merging #194 (c71e9ed) into main (f13dc86) will increase coverage by 0.05%.
The diff coverage is 86.20%.

@@            Coverage Diff             @@
##             main     #194      +/-   ##
==========================================
+ Coverage   58.25%   58.31%   +0.05%     
==========================================
  Files          58       58              
  Lines        3349     3351       +2     
==========================================
+ Hits         1951     1954       +3     
+ Misses       1269     1267       -2     
- Partials      129      130       +1     

Flag	Coverage Δ
unittests	58.31% <86.20%> (+0.05%)	⬆️

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

Impacted Files	Coverage Δ
pkg/confgen/flowlogs2metrics_config.go	0.00% <ø> (ø)
pkg/pipeline/pipeline_builder.go	59.50% <20.00%> (-0.43%)	⬇️
pkg/pipeline/encode/encode.go	100.00% <100.00%> (ø)
pkg/pipeline/encode/encode_kafka.go	66.66% <100.00%> (-1.13%)	⬇️
pkg/pipeline/encode/encode_prom.go	81.77% <100.00%> (+0.08%)	⬆️
pkg/confgen/grafana_jsonnet.go	0.00% <0.00%> (ø)
pkg/pipeline/ingest/ingest_collector.go	65.28% <0.00%> (+1.65%)	⬆️

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[mariomac]

Temporarily setting do-not-merge label since this is a breaking change that can break existing installations and RC release.

Let me work on a temporary solution to keep NOO working after we merge this change.

[mariomac]

Please let's coordinate merging this PR at the same time as: netobserv/network-observability-operator#93

[mariomac]

Unblocking the PR, after internally discussing and make sure that this won't break the next NOO release.

[KalmanMeth]

@mariomac Mario, Please merge this PR at the same time you perform the merge on https://github.com/netobserv/network-observability-operator/pull/93