Add ID to validation log messages

To distinguish what went wrong where, it would be helpful to add a short ID to any validation process log message.

This can be important e.g. when a repository has multiple validation hooks and the cloning and validation processes are running in parallel, spamming the log messages. Without ID it is basically impossible to distinguish which message came from which validation process.

Start by locating the validation-process log messages in the Go code and trace how validation runs are created or executed. Done means every validation process log message includes a short ID that distinguishes concurrent validation processes; the issue mentions no specific files or tests.

Written by the indexing model from the issue text.