Add BeaconDB as cell location provider

Thore Göbelrequested to merge
thgoebel/findmydevice:beacondb into master

Add BeaconDB (https://beacondb.net/) as a cell location provider. BeaconDB is automatically used when running fmd locate cell. I don’t want to add a new setting or option to not overload FMD.

Adresses https://gitlab.com/Nulide/findmydevice/-/issues/224.

Depends in !297 (merged) and !300 (merged).

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