NavSat / GPS sensor noise has wrong description? Or gz-sensors wrong implementation?

`navsat/horizontal` noise says the noise is in meters:

https://github.com/gazebosim/sdformat/blob/ed018d8758f475c3f0ec8247a5616b380f564856/sdf/1.12/navsat.sdf#L10

NavSat sensor in gz-sensors adds noise in degrees of lat/lon:

https://github.com/gazebosim/gz-sensors/blob/d266990ace6bb0d4da1ac79e55731d3b47890616/src/NavSatSensor.cc#L180

this->SetLatitude(GZ_DTOR(iter->second->Apply(this->Latitude().Degree())));

There is a related issue in https://github.com/gazebosim/gz-sensors/issues/325 .

We need to decide what is correct and what is not.

I'd vote for meters because that is how the error really manifests. Error in degrees of longitude has a different metric meaning for each latitude and is thus much less useful.

The migration consequences of choosing meters wouldn't be that bad. If somebody had specified noise of 1e-5 to get a +- meter precision, he'd end up with a super precise sensor. If we chose that degrees are correct, the user would end up with a GPS that jumps kilometers.

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To be precise, this is what gz-sim currently does:

- position:
- horizontal: degrees
- vertical: meters
- velocity:
- horizontal: meters/s
- vertical: meters/s

Compare the noise definition in sdf/1.12/navsat.sdf with the degree-based handling in gz-sensors/src/NavSatSensor.cc, and review the related gz-sensors issue 325. First establish whether horizontal position noise is specified in meters or degrees; done means the specification and implementation agree and the migration impact is resolved.

Written by the indexing model from the issue text.