enhancement: docker healthcheck

[goenning]

Issue: closes #363

• implements docker health check
• remove unused endpoints
• adds /-/health

[codecov-io]

Codecov Report

Merging #371 into master will decrease coverage by 0.58%.
The diff coverage is 12.9%.

@@            Coverage Diff             @@
##           master     #371      +/-   ##
==========================================
- Coverage   73.03%   72.45%   -0.58%     
==========================================
  Files          74       76       +2     
  Lines        4765     4766       +1     
==========================================
- Hits         3480     3453      -27     
- Misses       1031     1059      +28     
  Partials      254      254

Impacted Files	Coverage Δ
main.go	0% <0%> (ø)	⬆️
app/cmd/ping.go	0% <0%> (ø)
app/cmd/server.go	0% <0%> (ø)
app/pkg/web/engine.go	50% <100%> (ø)	⬆️
app/cmd/routes.go	100% <100%> (ø)
app/handlers/common.go	66.67% <50%> (-15.83%)	⬇️
app/pkg/log/logger.go	52.83% <0%> (-7.55%)	⬇️
app/pkg/web/context.go	78.72% <0%> (-0.85%)	⬇️

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