feat(webserver): add Prometheus

[genofire]

to run yanic with promtheus, you need both parts

• [webserver.prometheus] <- the exporter
• [[nodes.output.prometheus-sd]] <- service discovery to write json

example prometheus config to map the exporter (like blackbox-exporter)

  - job_name: 'yanic'
    metrics_path: /metric
    file_sd_configs:
      - files:
          - '/tmp/yanic.json'
    relabel_configs:
      - source_labels: [__address__]
        target_label: __param_node_id
      - source_labels: [__param_target]
        target_label: instance
      - target_label: __address__
        replacement: EXPORT_WEBSERVER:PORT
      - source_labels: [job]
        target_label: service

[codecov-commenter]

Codecov Report

Merging #189 (d7402fb) into main (7da4dc7) will decrease coverage by 1.91%.
The diff coverage is 53.49%.

❗ Current head d7402fb differs from pull request most recent head d506297. Consider uploading reports for the commit d506297 to get more accurate results

@@            Coverage Diff             @@
##             main     #189      +/-   ##
==========================================
- Coverage   73.10%   71.18%   -1.92%     
==========================================
  Files          55       59       +4     
  Lines        2406     2683     +277     
==========================================
+ Hits         1759     1910     +151     
- Misses        594      717     +123     
- Partials       53       56       +3     

Impacted Files	Coverage Δ
cmd/serve.go	6.00% <0.00%> (-1.15%)	⬇️
webserver/prometheus/config.go	0.00% <0.00%> (ø)
webserver/prometheus/exporter.go	0.00% <0.00%> (ø)
webserver/prometheus/transform.go	90.90% <90.90%> (ø)
webserver/prometheus/metric.go	100.00% <100.00%> (ø)
webserver/webserver.go	100.00% <100.00%> (ø)
database/all/internal.go	91.66% <0.00%> (-8.34%)	⬇️
database/all/connection.go	47.61% <0.00%> (-2.39%)	⬇️
output/meshviewer-ffrgb/meshviewer.go	84.84% <0.00%> (+4.04%)	⬆️