feat: Add GET /_health endpoint

[gfyrag]

Return 500 if not ok and 200 if ok.
The response will contains a map of string/string for each checks.
The value is 'OK' if the check passed, otherwise, is is the error.

[codecov]

Codecov Report

Merging #170 (60c4548) into main (3c42a79) will increase coverage by 0.25%.
The diff coverage is 87.50%.

❗ Current head 60c4548 differs from pull request most recent head 7204f54. Consider uploading reports for the commit 7204f54 to get more accurate results

@@            Coverage Diff             @@
##             main     #170      +/-   ##
==========================================
+ Coverage   73.97%   74.22%   +0.25%     
==========================================
  Files          76       79       +3     
  Lines        3093     3147      +54     
==========================================
+ Hits         2288     2336      +48     
- Misses        634      640       +6     
  Partials      171      171              

Impacted Files	Coverage Δ
internal/pgtesting/testing.go	86.95% <ø> (ø)
pkg/storage/sqlstorage/driver.go	71.83% <0.00%> (-3.56%)	⬇️
pkg/api/controllers/health_controller.go	93.54% <93.54%> (ø)
pkg/api/controllers/controllers.go	100.00% <100.00%> (ø)
pkg/api/internal/testing.go	98.26% <100.00%> (ø)
pkg/api/routes/routes.go	100.00% <100.00%> (ø)
pkg/health/health.go	100.00% <100.00%> (ø)
pkg/health/module.go	100.00% <100.00%> (ø)
pkg/ledger/resolver.go	85.00% <100.00%> (ø)
pkg/ledgertesting/db.go	88.09% <100.00%> (ø)
... and 2 more

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