TUF file version

[andreabedini]

Reading this passage in hackage-server source code made me notice we might not be doing TUF file versions correctly; we always say FileVersion 1.

https://github.com/haskell/hackage-server/blob/613f5eb2f24d6ccbdef349d65f38247425ab64df/src/Distribution/Server/Packages/Metadata.hs#L23-L49