bug(http_metrics): fix incorrect metrics type

[rustatian]

Reason for This PR

closes: #162

Description of Changes

• Change rr_http_requests_queue type from Summary to Gauge.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.] [Reviewer TODO: Verify that these criteria are met. Request changes if not]

• [x] All commits in this PR are signed (git commit -s).
• [x] The reason for this PR is clearly provided (issue no. or explanation).
• [x] The description of changes is clear and encompassing.
• [x] Any required documentation changes (code and docs) are included in this PR.
• [x] Any user-facing changes are mentioned in CHANGELOG.md.
• [x] All added/changed functionality is tested.

[codecov[bot]]

Codecov Report

Merging #163 (3d49c0a) into master (8440cb5) will decrease coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #163      +/-   ##
==========================================
- Coverage   67.40%   67.38%   -0.02%     
==========================================
  Files         134      134              
  Lines       10477    10477              
==========================================
- Hits         7062     7060       -2     
- Misses       2675     2677       +2     
  Partials      740      740              

Impacted Files	Coverage Δ
http/middleware/prometheus/plugin.go	95.69% <100.00%> (ø)
beanstalk/beanstalkjobs/item.go	73.97% <0.00%> (-2.74%)	:arrow_down:

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