Add rsofun demo driver data generation script

[stineb]

Add a script analysis/05_generate_demo_rsofun_drivers.R that should generate the demo driver data based on updated FDK files.

The demo driver data needs updating with the following aspects addressed:

• [x] net radiation as an input added to forcing
• [x] ccov_int removed
• [x] model parameters synced based on latest rsofun

Note that certain variables need to be derived from the half-hourly data. This has implication for the downsampling function but I'm not sure how this is not handled.

• [x] tmin: minimum of half-hourly temperature values for each day
• [x] tmax: maximum of half-hourly temperature values for each day

Should keep in mind that we define the following as we did before. This has also implication for the downsampling function but I'm not sure how this is not handled.

• [x] VPD as daytime average, determine 'daytime' based on half-hourly top-of-atmosphere solar radiation
• [x] temperature as daytime average, determine 'daytime' based on half-hourly top-of-atmosphere solar radiation

[stineb]

Daytime averages added per PR https://github.com/geco-bern/FluxDataKit/pull/60

[stineb]

All points addressed by PR https://github.com/geco-bern/FluxDataKit/pull/60