Add marker and markersize keywords to plot_radar_position()

[billetd]

Scope

This PR simply adds marker and markersize keywords to plot_radar_position() so that the markers themselves can be controlled. Right now that is just control of their size and shape. Shapes are based on those available to ax.scatter() (see matplotlib docs)

Approval

Number of approvals: 1

Test

import pydarn
import cartopy.crs as ccrs
import cartopy.feature as cfeature
import datetime as dt

# Setup a zoomed in geographic axis
ax, _ = pydarn.plotting.projections.axis_geographic(dt.datetime(2024, 10, 9), plot_center=[-100.2, 70], plot_extent=[40, 40], grid_lines=False)

# Add coloured landmasses for a nice aesthetic 
land_50m = cfeature.NaturalEarthFeature('physical', 'land', '50m', edgecolor='black', facecolor='ivory', linewidth=0.2)
ax.add_feature(land_50m, zorder=0)

# Plot red stars at all northern hemisphere radars except those that are decommissioned (see https://superdarn.ca/radar-info)
for stid in pydarn.SuperDARNRadars.radars.keys():
    if pydarn.SuperDARNRadars.radars[stid].hemisphere == pydarn.Hemisphere.North:
        if stid not in [2, 8, 9, 10]:
            pydarn.Fan.plot_radar_position(stid, ax=ax, date=dt.datetime(2024, 10, 9), coords=pydarn.Coords.GEOGRAPHIC, projs=pydarn.Projs.GEO, transform=ccrs.PlateCarree(), marker='*', markersize=10, line_color='red')

Output: