Importer logging improvements

Problem

While working on &7528 (closed), I noticed a few minor issues in the Importer logs:

• The repository log key is not always set to the repository full path but rather a mix between path and name: !945 (merged)

• We're lacking an importing configuration message, similar to what we have for importing layer. Currently, we only have a blob transfer complete message for the config blob. If the config is already present then we have zero log messages: !943 (merged)

• We're missing a blob already present, no need to transfer log message whenever we action the transfer service for a blob that already exists on the new code path. This log message existed a while ago (3366b1d0) but was reverted. Bring it back. !944 (merged)

• The tag log key is overridden in ELK on .com with the path to the registry log file. We should rename it to something else: !940 (merged)