allocate a virtual machine in google cloud

See merge request !3

update ci/cd pipeline to build and push docker images

See merge request !1

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