Ignore negative workload latency

[tanveergill]

Issue

• Workload latency in case of Envoy is calculated as:

workload_latency = response_latency - aperture_latency

• Workload Latency can become negative in case of connection reset
  • If the connection is aborted by Client or Server Envoy immediately terminates the connection for the other endpoint.
  • In the Access Log, status code is set as 0 and response_latency is set as zero.
  • If Authz call to Aperture Agent had succeeded for this request, then aperture_latency is greater than zero.
  • This would lead the workload_latency to be computed as negative.
    

Fix

• Ignore negative workload latency I.E. don't populate the workload latency column
• Publish Prometheus metrics for flux-meter or workload latency only if the metric column is found

Checklist

• Tested in playground or other setup

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This change is 

[codecov]

Codecov Report

Base: 37.45% // Head: 3.36% // Decreases project coverage by -34.09% ⚠️

Coverage data is based on head (087f62e) compared to base (367c5c8).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #839       +/-   ##
==========================================
- Coverage   37.45%   3.36%   -34.10%     
==========================================
  Files         278     278               
  Lines       20494   20499        +5     
==========================================
- Hits         7677     689     -6988     
- Misses      12337   19742     +7405     
+ Partials      480      68      -412     

Impacted Files	Coverage Δ
...ollector/metricsprocessor/internal/envoy_labels.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/otelcollector/metricsprocessor/processor.go	0.00% <0.00%> (-65.12%)	⬇️
pkg/status/provide.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/notifiers/event.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/etcd/notifier/key.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/platform/readiness.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/config/unmarshaller.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/etcd/notifier/prefix.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/policies/common/paths.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/notifiers/basic-notifier.go	0.00% <0.00%> (-100.00%)	⬇️
... and 159 more

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