Metrics added

[tarampampam]

Description

Added

• HTTP route /metrics with metrics in prometheus format
• Comment in generated script with "script generation" time

Fixes #37

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I wrote unit tests for my code (if tests is required for my changes)
• [x] I have made changes in CHANGELOG.md file

[codecov[bot]]

Codecov Report

Merging #95 (120cbea) into master (681b3a3) will increase coverage by 0.27%. The diff coverage is 89.09%.

@@            Coverage Diff             @@
##           master      #95      +/-   ##
==========================================
+ Coverage   86.31%   86.58%   +0.27%     
==========================================
  Files          31       34       +3     
  Lines        1001     1051      +50     
==========================================
+ Hits          864      910      +46     
- Misses         76       78       +2     
- Partials       61       63       +2     

Impacted Files	Coverage Δ
internal/pkg/http/server.go	80.48% <50.00%> (+0.48%)	:arrow_up:
internal/pkg/http/routes.go	87.50% <75.00%> (-2.75%)	:arrow_down:
internal/pkg/metrics/generator.go	91.30% <91.30%> (ø)
internal/pkg/http/handlers/generate/handler.go	77.33% <100.00%> (+0.83%)	:arrow_up:
internal/pkg/http/handlers/metrics/handler.go	100.00% <100.00%> (ø)
internal/pkg/metrics/metrics.go	100.00% <100.00%> (ø)
internal/pkg/version/version.go	100.00% <100.00%> (ø)

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