Add support for kopia-assisted incremental backups

[ashmrtn]

Getting incremental backups in corso requires a few changes to kopia itself. This tracks all the sub-issues required to get incremental backups enabled.

• Create patch allowing user to set StreamingFile timestamps in kopia #512
• Upstream patch allowing user to set modified time in StreamingFile in kopia #513
• Modify kopia uploader to ignore some StreamingFile metadata fields for equality checks #514
• upstream kopia uploader StreamingFile checks #515
• update kopia to version including StreamingFile caching code #615
• modify corso's kopia wrapper code to set mod time on StreamingFiles #621
• pass last modified time from graph connector to kopia wrapper #622
• Fetch previous kopia snapshots rooted in the same directory during backup #1404
• Delay fetching Exchange item data from Graph API until it's clear kopia will be uploading the item #2023

[ashmrtn]

closing for now as there are proposals for other changes that would affect how and when item information is fetched