added flushImmediate to audioPreference options

[krseager]

This PR will add the ability to set the default behavior of audio track switching to default to smooth or immediate audio track switching.

Why is this Pull Request needed?

Without it, you have to conditionally call the setting of nextAudioTrack vs. audioTrack for differentiating between smooth and immediate audio track switching.

Are there any points in the code the reviewer needs to double check?

Resolves issues:

#7692

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md

[robwalch]

#7692 describes enhancing hls.setAudioOption({}) not the hls.audioTrack setter. The preference argument with the flush option would passed to the setAudioOption method rather than set on the player config and read on each call.

Without it, you have to conditionally call the setting of nextAudioTrack vs. audioTrack for differentiating between smooth and immediate audio track switching.

That’s intentional. The different audio setters should continue to work as they do, similar to the level setters.