feat(plugins/stargazers): support alternative geocoding service

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Discussed in #1149

^{Originally posted by jayvdb July 22, 2022}
The stargazers plugin now supports a map visualisation which looks really good. However I would rather not set up a Google Billing account for it.

I think it would be useful to add support for alternative services, especially OpenStreetMap Nominatim which has lots of providers some with reasonable free daily limits, including MapQuest which has a free limit of 15,000 per month. The base url endpoint could be a setting so that the user can choose which provider works best for them. Most JS Nominatim clients support this.