core: frontend: vehicle-setup: allow controlling Sea-level GPS for boats

### Current behaviour

BlueBoat defaults [`GPS_NAVFILTER`](https://ardupilot.org/rover/docs/parameters.html#gps-navfilter-navigation-filter-setting) to Sea, which works well for standard users but not for those operating in water bodies at elevation (e.g. rivers/lakes on mountains).

As the parameter is set by default, for those users it just seems like the GPS isn't working, and they have no idea why.

Some relevant [internal discussion](https://bluerobotics.slack.com/archives/CP7Q82NDB/p1776706830238829).

### Expected or desired behaviour

We should make it possible to configure through the vehicle setup page, with an intuitive explanation about when you would want it on vs off.

### Prerequisites

- [x] I have checked to make sure that a similar request has not already been filed or fixed.