set skins via env var

[fragolinux]

Describe the solution you'd like can we set skins via env var? This way there's no need to create symlinks pointing to a skin (with the cluster context in its filename), and can easily be set and changed via envrc files, defaulting to standard skin if env missing/wrong or skin not present/downloaded

[trever-atr]

this would be so great. i manage multiple contexts via shell sessions and would like to a var like K9S_SKIN, instead of fiddling with another set of context-specific config files

[trever-atr]

this has been completed with https://github.com/derailed/k9s/pull/3356.