Support src coming from the source element in media-tracking

[igneel64]

Currently the media-tracking plugin does correctly retrieve the media source from a setup using the <source /> element. E.g. for the below case, the src attribute will end up as empty which is not allowed on the media schema.

 <audio id='audio-id'>
      <source
        src="https://snowplow.com/test.mp3"
        type="audio/mp3"
      />
</audio>

Describe the solution you'd like Support this case properly. We know that the src and currentSrc will end up the same in all those cases, but this is expected.

Describe alternatives you've considered Changing media structures is daunting for a setup.