Update primary field argument passed to ElectrostaticSphere

[santisoler]

Use an array with 3 elements instead of a float as the primary_field argument for the ElectrostaticSphere. Geoana errors out if a float is passed instead.

[santisoler]

@lheagy I think this solves the error that Geoana raises. Please, check that the values for the primary field are correct.

[lheagy]

Thanks Santi! It looks like this now runs, but the results for the electric field and the current density look off

e.g. currently on the site
https://em.geosci.xyz/content/maxwell2_static/fields_from_grounded_sources_dcr/electrostatic_sphere.html#electric-field

and now

This might be a bug down in geoana. The potentials look correct though

[lheagy]

I was hoping this would be obvious, but it will take some more time to figure out where things went sideways here. What do you think of pinning to an older version of geoana for now so that we can get #577 in, @santisoler?

[santisoler]

Sure! Let's pin it. We can solve this later on.