Sensor_Audio: Add Knowles_LGA-3_2.75x1.85mm.kicad_mod

This package is used by MEMS microphones such as

https://www.knowles.com/docs/default-source/default-document-library/spv1142lr5h-1_quartz_datasheet.pdf

Note that the package has 4 pins, but pin 4 is not present in the recommended landing pattern. I added it nevertheless so routing is restrained in that area.