We've seen multiple occurences lately on several devices where playback
failed after playing a few encrypted contents.

On those, setting the `closesSessionsOnStop` option (an option and
already-existing work-around) had no effect, yet renewing the MediaKeys
at each load fixed the issue.

It's very probably a device bug. For those, we usually had the strategy
of knowing on which devices this problem was encountered, detect it
inside the RxPlayer, and choose to always renew the `MediaKeys` on those
(without the application even knowing we did that).

However, some users suggested to us to add this as an option, because
they may have reproduced the issue on other devices.

I'm kind of ambivalent toward adding this as an option:

  - I generally prefer our strategy of fixing it for all devices with the
    issue, with people reporting issues to us when a new device has the
    issue. This allows to fix it once and for all for all those devices.

  - I understand that some applications might prefer to iterate rapidly
    and be able to have more control over the RxPlayer behavior.

Another PR, #1510, would allow doing this by patching our config instead
but this would not be doable in production for applications (config
properties are not something we guarantee in our API).

This PR however, would allow applications to do it when and wherever they
please.

Thoughts?