Load files using Dagger

[Balinus]

By using Dagger, we could load files in parallel.

See here for example: https://github.com/JuliaComputing/JuliaDB.jl/blob/8bf3057df154b7d0b592248bb3be98171dd28738/src/io.jl#L90

[Balinus]

Should be possible with NCDatasets v0.5.1 https://github.com/Alexander-Barth/NCDatasets.jl/releases/tag/v0.5.1