Add font size option for circle marker

[giswqs]

Fix #627

import leafmap.foliumap as leafmap

m = leafmap.Map(center=[40, -100], zoom=4)
data = "https://raw.githubusercontent.com/opengeos/leafmap/master/examples/data/us_cities.csv"
m.add_circle_markers_from_xy(
    data, x="longitude", y="latitude", radius=10, color="blue", fill_color="black", font_size=5
)
m

[github-actions]

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