Support for motor (async pymongo)

**Is your feature request related to a problem? Please describe.**
The Python Elastic APM agent does not automatically instrument async calls to mongodb using motor

**Describe the solution you'd like**
Support for automatic instrumentation of motor similar to the way pymongo is instrumented

**Describe alternatives you've considered**
For now we have lived without instrumentation, although it looks like it should be possible to adapt the pymongo wrappers

**Additional context**
This is the motor project: https://github.com/mongodb/motor
It should be similar to pymongo