Fix leftover/extra index volume after interrupted upload and more tests

[Jojo-1000]

• Fixes part of recreate "Remote file referenced as ..." error after interrupted backup then compact #5023
• Also adds more test cases to track some known reproducible issues (those that fail are category "Bug" and explicit only).

Steps to reproduce

• See IssueTests.Issue5023ReferencedFileMissing and RepairHandlerTests.RepairExtraIndexFiles

Current behavior

• After interrupted dindex upload (but the upload finished), no index-block link is created
• The next run uploads a new dindex file for the dblock
• When repairing with an extra index file, the invalid ID -1 is inserted into the link table

New behavior

• Index-block link is always created
• The next run recognizes that the dindex file already exists and no extra is uploaded
• When repairing with an extra index file, the correct ID is inserted into the link table

Impact

• Order of operations in repair handler was changed to fix the ID bug, but wrapped in a transaction to ensure that no inconsistencies occur.
• The index block link is created before the upload is known to be completed (instead of after the upload). It will be removed together with the RemoteVolume entry at the start of the next run.

[duplicatibot]

This pull request has been mentioned on Duplicati. There might be relevant details there:

https://forum.duplicati.com/t/how-to-fix-missing-volumes/17377/14