Feature: cache some command answers to avoid having to repeat them

[XaF]

Commands such as asdf update, or listing of a specific plugin available versions should be commands that should be cacheable. It would allow omni up to go faster when doing it on multiple repositories using common dependencies for instance.

Something like bkt's retrieve_streaming could allow us to keep the current UI while having bkt handling the caching for us. We could put the stored information in the temp directory of the OS, to be emptied upon reboot.

[XaF]

Fixed by 946d1f0

Discarded using bkt as decided to go for more intentional caching vs. command output caching.