Display dataset used storage

[fm3]

Show used storage of datasets.

Steps to test:

• provoke a storage scan by setting both fetchUsedStorage.rescanInterval and fetchUsedStorage.ticketInterval to 1 minute, and reportUsedStorage.enabled to true
• in dashboard, click on a number of datasets to check displayed size (should be hidden for remote datasets)

TODOs:

• Backend
  • include used storage in dataset json
• Frontend
  • display the info in the sidebar of the dataset list in dashboard
  • hide values <10KB to avoid confusion

Issues:

• fixes Show dataset storage size in dataset list #7662

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• Updated changelog
• Considered common edge cases

[philippotto]

I think, showing the bytes in the tooltip doesn't really add a value. I'd rather say something like "Note that linked layer's aren't measured" or something like that.