Save Digital Read and Analog Read data to BDF file

[retiutut]

Is your feature request related to a problem? Please describe.

Currently, only Accelerometer and EXG channels are added to BDF file

Describe the solution you'd like

Find a way to add Digital Read (5 channels) and Analog Read (3 Channels) to BDF file. We may need to have all three Aux data types included in BDF files since users could possibly change modes during a session or even during a live recording.

Describe alternatives you've considered

We have only saved Accelerometer data to BDF file for many years.

Additional context

This will help users who would like to work with MNE.

[retiutut]

https://openbci.com/forum/index.php?p=/discussion/3303/accessing-analog-channel-data-when-recorded-in-bdf-format#latest

[retiutut]

Keep this as High Priority and to be included in 5.1.0.