broadcast.go: on detection of low video output issues lower bitrate to accommodate

[Saxon Milton]

When we detect low video output errors during health checks we could gradually lower the video bitrate value to accomodate. It’s been noted that often when these sorts of errors arise, we can reduce their severity by decreasing the bitrate, indicating that it’s likely due to a sub optimal misalignment of the CPE infrastructure or occasional network upload issues beyond our control.