Log more details about partitions

Gitaly is currently logging a repository's relative path instead of a partition's ID when a partition fails. This is a remnant from the past before partitions when each repository had its own transaction manager. These days we should rather be logging the ID of the partition. Include the partition ID as field in the logger.

Additionally, if the partition fails, include the state directory of the partition as a field. This makes it easier to locate the state of the partition having issues.