feat: set media player preference as enabled by default

[ayoayco]

Proposal to promote the media player as not experimental 😄

We decided to put this feature as experimental to gather feedback and bug reports. I looked through the issues to see if there are complaints regarding the media player, but there seems to be none! 🎉

This PR will

• set the preference to show embedded media player as true by default
• promote embedded media player as not experimental

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[userquin]

Restore old experimental value and delete it once the new preference saved (the problem, we don't know if the user has disabled the experimental feature so we need to restore the original value if experimental still there, otherwise we don't need to change the new feature since it is enabled by default)

/cc @patak-dev @shuuji3

[ayoayco]

I will check, thanks!!