Although, password file is checked during config validation, sth may have changed the
file content in the short period of time between validation and DB client initialization,
hence exiting in case of an error

* new slog in stdlib is utilized for that and replaces 'log' pkg
* configuration pkg is used validate and now set/define/refer
  log level values
* the 'error' level call is not fatal, thus os.Exit is called
  instead

See https://github.com/prometheus/docs/blob/496a6ee5ffea8a08f42f98cc7208256d300be015/content/docs/instrumenting/exposition_formats.md

* remove some spaces
* return item.Name() instead of map key
* re-order router log output

THis change set aims to simulate running test as if they
would be executed in a pipeline

The location where the actual items should reside is in the store, while
only references are being returned when attempting to access an item.

Fore more information see https://go.dev/blog/maps#concurrency

Somebody havent heard about SemVer yet. The Ctx.GetReqHeaders() return value
slightly changed (string to []string), which now requires to first join the slice
before checking whether it contains the given string