Offer to import session from previous versions

[ahcm]

Hi,

zellij now stores the sessions in a versioned subfolder (~/.cache/zellij/$VERSION/session_info).
I upgraded to 0.40.1 from 0.39.2 and copied the folder's contents over and it worked.
But I guess it would be better to offer a supported way for users, especially in the case of incompatiblities.

Best
Andreas

[merikan]

duplicate of #3371 ?

[ahcm]

I filed it as enhancement though :-)