Fixed event handler for displaying comments and adding markers to the timeline

[jp-rad]

Fixed event handler for displaying comments and adding markers to the timeline

#694

Description

Changing loadedmetadata event to loadeddata event, because called after initialize().

initialize()
https://github.com/mediacms-io/mediacms/blob/main/frontend/src/static/js/components/comments/videojs-markers.js#L454

The original onCommentsLoad function was separated into the onCommentsLoad function and the retrieveComments function.

[mgogoulos]

Hi @jp-rad
I've checked out this PR and have the following questions:

1. Is this ready to be merged or you have concerns? Not sure I understand what is the case on TIMESTAMP_IN_TIMEBAR does not work. #694 (comment)
2. The big problem remains after update to latest video.js and is the fact that when you visit a media URL that has timestamp, the video starts on this timestamp but IMMEDIATELY afterwards goes back to the beginning. This behaviour wasn't happening before. Do you have any idea how this can be fixed?