praefect: Migrate track-repositories sub-command

Migration of the 'track-repositories' sub-command from the old implementation to the new approach with usage of the third party urfave/cli/v2 third party library. The invocation of the command remains the same, but it has more descriptive representation when help is invoked. Also, it is possible now to invoke help only for the sub-command to see more details about it and its usage.

The old sub-command helper functions are not needed anymore as all old-fashioned sub-commands now replaced with the new.
Also, we don't need to modify a help text for praefect command anymore to include old-fashioned sub-commands and restrict 'serve' sub-command to not accept arguments.

Closes: #5001 (closed)