fix(bug): do not write internal error to the users responseWriter

[rustatian]

Reason for This PR

closes: #691
closes: #659

Description of Changes

• Handle internal errors and write only status code to the user. The original error would be in the logs.
• Handle SoftJob errors and send them w/o modifications to the logger.
• Add new options to the HTTP config: internal_error_code to override default 500 internal HTTP error code (useful for the LB).

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 #700 (7daadf3) into master (9c01e7a) will increase coverage by 0.22%.
The diff coverage is 83.63%.

@@            Coverage Diff             @@
##           master     #700      +/-   ##
==========================================
+ Coverage   69.15%   69.37%   +0.22%     
==========================================
  Files          91       91              
  Lines        4422     4451      +29     
==========================================
+ Hits         3058     3088      +30     
  Misses        969      969              
+ Partials      395      394       -1     

Impacted Files	Coverage Δ
pkg/worker_watcher/worker_watcher.go	85.71% <ø> (ø)
pkg/worker_handler/request.go	80.95% <33.33%> (+0.30%)	⬆️
pkg/worker/sync_worker.go	77.08% <42.85%> (ø)
pkg/worker_handler/handler.go	69.89% <86.95%> (+5.33%)	⬆️
pkg/pool/static_pool.go	80.95% <100.00%> (+0.13%)	⬆️
pkg/worker/worker.go	90.66% <100.00%> (+0.12%)	⬆️
pkg/worker_handler/response.go	88.88% <100.00%> (+0.31%)	⬆️
plugins/http/config/http.go	57.81% <100.00%> (+1.36%)	⬆️
plugins/http/plugin.go	81.92% <100.00%> (+0.20%)	⬆️
plugins/server/plugin.go	62.01% <100.00%> (+1.35%)	⬆️
... and 1 more

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