New 'praefect configuration validate' sub-command for Praefect

In order to improve developers experience in using Praefect the new 'configuration' sub-command is added. It now has only one sub-command 'validate' to validate provided configuration before starting the service. Now only cli is implemented and there is no real check of the configuration. The command always succeeds if file in the proper toml format is provided no matter what content it has.

Part of: #4650 (closed)