add ESA driving functions docstring examples for dipoles

[fs446]

There are ESA driving functions that use dipole secondary sources: def esa_edge_dipole_2d_line def esa_edge_dipole_2d_plane

We need to add these to the new handling, i.e. something like def secondary_source_line_dipole(omega, c): We need to add/update docstring examples for these cases.