Add APIs to retrieve magnetometer data

[mazar-farran]

Ticket: https://github.com/Hivemapper/hdcs_firmware/issues/70

Added /magnetometer/:n endpoint and extended querySensorData to retrieve magnetometer data. Added magnetometer data to the /sensorquery endpoint.

• [X] Add a link to the ticket in the PR title or add a description of work in the PR title
• [X] dashcam firmware was loaded on a device and successfully runs
• [ ] semantic version was incremented inside src/config/index.ts