Exchange delta token-based incremental backups

[ashmrtn]

Reduce the number of Graph API requests for a backup as well as the amount of time a backup takes by leveraging delta tokens in Exchange. This ticket addresses only incremental backups. It does not address restartability at all

This feature requires work on multiple components and includes the following:

• Use delta endpoint to fetch item IDs during backup #1612
• persist M365 delta token #1685
• Update interfaces for incremental backups #1700
• Fetch previous kopia snapshots rooted in the same directory during backup #1404
• Split CLI backups of multiple (resource owner, service) to separate backups #1505
• Add logic for merging directory hierarchies for incremental backups #1740
• GC should re-use delta tokens in Exchange when they're provided #1725
• GC should accept id->path lookup collections on backup #1726
• GC should fulfill new Collection interface additions in Exchange when populating backups #1727
• return reason why a snapshot was selected as a base for an incremental backup #1779
• logic to fallback to a full backup if a delta token has expired #1780
• BackupOp must pass complete tag set to kopia.Wrapper during BackupCollections #1781
• merge backup details from base snapshot(s) and items in Collections #1800
• fallback to full backup of container or data category if metadata is incomplete/missing #1804
• only select relevant metadata from each base snapshot #1829
• pass relevant subtrees to use in base from BackupOp to kopia.Wrapper #1832
• fetch changes to emails even if the change is just [un]marking read flag #1866
• don't source items from base snapshot if collection is marked as new #1884
• add NoMerge flag for collections to control merging in kopia #1914

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Testing

• Incrementals e2e/integration tests #1966
• Incrementals Mocked GC Tests #1967

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Phase 2

• add flag to force full backup #1901
• properly handle isRead status changes in Exchange mail #1865
• do not allow backups with no details snapshot to participate as a base in an incremental backup #1878
• Update Backup Details schema to indicate if an item was updated in a Backup #1812
• precheck to ensure every (resource owner, service, category) tuple is unique across all bases #1945
• Fine-grained supply of delta incrementals #2068
• Incrementals - Calendar Event Delta Handling #2022
• Ensure data collections don't have repeated items #1954

[ashmrtn]

closing as remaining issue is tracked elsewhere