Fix: Error immediately when metrics export server fails

[JoshVanL]

The metrics exporter will currently now immediately error if the server listener fails, for example if the port is already being used, and will therefore silently hang.

PR makes the metrics exporter fail immediately and return.

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (648ac48) 64.86% compared to head (19260d6) 64.87%.
Report is 1 commits behind head on master.

❗ Current head 19260d6 differs from pull request most recent head 45099bc. Consider uploading reports for the commit 45099bc to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7021      +/-   ##
==========================================
+ Coverage   64.86%   64.87%   +0.01%     
==========================================
  Files         231      230       -1     
  Lines       20840    20784      -56     
==========================================
- Hits        13518    13484      -34     
+ Misses       6186     6166      -20     
+ Partials     1136     1134       -2     

Files	Coverage Δ
pkg/metrics/exporter.go	31.81% <0.00%> (-3.19%)	⬇️

... and 12 files with indirect coverage changes

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