Allow changing the communication format for I2S output

[whc2001]

Some I2S DACs (like the cheap PT8211 and the even cheaper clone TM8211) use the Least Significant Bit Justified (LSBJ) communication format instead of the standard I2S format. At the DAC's native bit depth (16 bit), it is essentially the same timing as Most Significant Bit Justified communication format, which can be selected by setting i2s_config.communication_format to I2S_COMM_FORMAT_STAND_MSB instead of I2S_COMM_FORMAT_STAND_I2S.

I have done this to the ESP32 version of the SnapCast client, however there I implemented as a menuconfig entry. However here all the output config is expressed with the config string (model=I2S,...). I wonder if I should implement wrt this as well? Something like comm_fmt=msb