mod_opusfile: Append recordings, support additional features

[mishehu]

The current mod_opusfile in tree does not support the ability to append to an existing recorded file. It also doesn't record any of the optional metadata (i.e. items defined by switch_audio_col_t), or the ability to make use of the different samplerates for encoding in order to target a sensible bitrate for the output file.

I have added this support, and am going to attach a PR here to this ticket.

[mishehu]

Pull request here:

#2709