Add option to use browser geolocation feature to locate city

[e-alfred]

It would be great to have the ability to use the geolocation feature of the browser to find the current city somebody is located in. This would ease searching and adding cities and make it more convenient for users who travel a lot for example. It is also something that could improve #83.

[almereyda]

This is also available in the official weather_status app bundled with nextcloud/server. This happens completely client side:

https://github.com/nextcloud/server/blob/777fe3bf18f2a6c6887d623eb889cc7895823ebe/apps/weather_status/src/App.vue#L274-L281

https://github.com/nextcloud/server/blob/777fe3bf18f2a6c6887d623eb889cc7895823ebe/apps/weather_status/src/App.vue#L313-L320

Eventually one could even share some basic methods with them, despite them using another API provider.

https://github.com/nextcloud/server/blob/e10cad4a718422b8b9d19546cc61cb39e4c0ee26/apps/weather_status/lib/Service/WeatherStatusService.php#L383