Add Footprint and Layout for Battery Connector (BT-003BE)

[slintak]

This pull request adds the footprint and layout placement for the battery connector used to connect the 2S Li-ion battery to the main PCB.

Summary of Changes

• Added footprint and 3D model for the BT-003BE battery connector. Product link: https://www.jbl-ec.com/bt-003be-3-way-spring-battery-connector-4-1mm-pitch-smt-product/
• Assigned the footprint to the battery connector in the schematic
• Positioned the connector in the PCB layout in the same place as original Retevis C62 PCB