fix map plots with custom user options

[megies]

What does this PR do?

Fixes map plots with user specified options like custom "projection" kwarg. These weren't properly passed through to the new helper method for initial cartopy plot setup, so default values were always winning.

Why was it initiated? Any relevant Issues?

fixes #3191

PR Checklist

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[megies]

https://docs.obspy.org/pr/fix_map_plot_initial_setup/packages/autogen/obspy.core.inventory.inventory.Inventory.plot.html

Looks good again..