Import cross signing recovery key from Element

[tinywombat765]

Is your feature request related to a problem? Please describe.
I'm writing a bot. I want to be able to provide the bot with the cross signing recovery key from Element, then have it grab all the room keys from the server. Looking at the documentation, this doesn't currently seem to be possbile but I might have missed something.

Describe the solution you'd like
I like to be able to import the recovery cross signing key from Element.

Describe alternatives you've considered
Only using emoji verification is workable but would be much less convient.

Additional context
NA

[poljar]

Sorry, that's not possible as of yet. Not sure when I'll get to it, hopefully before the end of the year.

I think that this can be closed as a duplicate of #402.