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

Initially, that was done to prevent flaky test runs, which turned out
to be caused by Fiber's behaviour (se previous commit).

Using the Param "name" to create an Item and persist turns out to be
affected bi Fiber's behaviour of "zero allocation", which means values
may be re-used across requests/contexts.

This caused wrong or chunked up Item names in the ephemeral state, which
only surfaced during unit testing.

For more details see https://docs.gofiber.io/#zero-allocation

This is to improve/funnel potentially fatal errors

* rework indentation of some configuration variables
* rename some 'err' variables to '_' since they are not used