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.