kubectl: rename k alias (#7749)

This uses `ku` instead of `k` as an alias for kubectl.

Fixes #6408

plugins/kubectl/kubectl.plugin.zsh

@@ -10,8 +10,7 @@ if (( $+commands[kubectl] )); then
     unset __KUBECTL_COMPLETION_FILE
 fi
 
-# This command is used a LOT both below and in daily life
-alias k=kubectl
+alias ku=kubectl
 
 # Execute a kubectl command against all namespaces
 alias kca='f(){ kubectl "$@" --all-namespaces;  unset -f f; }; f'