Update recording filename per app session or per recording

During testing, at one point I ran into an issue where the recording functionality stopped working. After a bit of debugging, the issue turned out to be that too many recordings over the same file on the device caused it not to be understood by AWS Lex.

To protect against this scenario, we could easily make the recording filename based on some identifier for the app session (even just a random string) or a timestamp. But I've only seen this issue manifest once after extensive testing, so I'm just opening this issue for visibility in case it occurs again.