- Have `openBackupCursor` accept as input: `incrementalBackup: <false/true>`.
- For backwards compatibility, the default value is false.
- The first full backup meant for incremental must pass true.
- All incremental backups (obviously) must pass true.
- Have `openBackupCursor` accept as input `thisBackupName: <string>`.
- This input exists iff `incrementalBackup: true`.
- The API should return a validation error if the name is not unique (for the "recent history" if provided names).
- Have `openBackupCursor` accept as input `srcBackupName: <string>`.
- This input must not exist when `incrementalBackup: false`.
- This input may or may not exist when `incrementalBackup: true`.
- The API should return a validation error if the `srcBackupName` is not in the "recent history" of provided `thisBackupName` s.