Make ArchiveDiffer log what mode it's in #1775
Description
ArchiveDiffer logs don't clearly indicate whether it's running in S3 mode or in filesystem mode, which makes it nearly impossible to reconstruct events if something has gone wrong during patching operations.
We should change the ArchiveDiffer to either add a log statement declaring the mode, or modify all ArchiveDiffer log statements to include the mode as one of the key-value pairs.