Add open-meteo.com as new weather source

[markusr]

Thank you for your work.

Open-meteo provides a 15-Minutely forecast for the following variables:

• Shortwave Solar Radiation GHI
• Direct Solar Radiation
• Diffuse Solar Radiation DHI
• Direct Normal Irradiance DNI
• Global Tilted Radiation GTI
• Terrestrial Solar Radiation

see https://open-meteo.com/en/docs/

It would be nice to use these values in PVForecast.

[StefaE]

Hi Markus,
thx for the pointer - this looks very interesting indeed and I'm planning to implement open-meteo as an additional provider. Expect some delays though, as I'm not at a very predictable schedule right now ... :-(