fix(various): Small fixes before release

[rustatian]

Reason for This PR

closes #557
closes #556

Description of Changes

• Remove unneeded mutex from the http.Workers method.
• Rename checker plugin package to status, remove /v1 endpoint prefix ([RR2, FEATURE REQUEST] Remove v1 in checker plugin #557)
• Add static, headers, status, gzip plugins to the main.go.
• Update tests

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]

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

[codecov]

Codecov Report

Merging #559 (fdbf6a6) into rc.4-release (7dc61c3) will decrease coverage by 0.06%.
The diff coverage is 80.00%.

@@               Coverage Diff                @@
##           rc.4-release     #559      +/-   ##
================================================
- Coverage         68.15%   68.08%   -0.07%     
================================================
  Files                65       65              
  Lines              3300     3293       -7     
================================================
- Hits               2249     2242       -7     
  Misses              766      766              
  Partials            285      285              

Impacted Files	Coverage Δ
plugins/gzip/plugin.go	100.00% <ø> (ø)
plugins/status/rpc.go	77.77% <ø> (ø)
plugins/http/plugin.go	68.88% <75.00%> (-0.57%)	⬇️
plugins/status/plugin.go	63.93% <80.00%> (ø)
plugins/static/plugin.go	76.19% <100.00%> (-0.56%)	⬇️

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