feat(helmfile): introduce helmfile plugin

plugins/helmfile/helmfile.plugin.zsh

@@ -0,0 +1,18 @@
+# Completion
+if (( ! $+commands[helmfile] )); then
+  return
+fi
+
+# If the completion file doesn't exist yet, we need to autoload it and
+# bind it to `helmfile`. Otherwise, compinit will have already done that.
+if [[ ! -f "$ZSH_CACHE_DIR/completions/_helmfile" ]]; then
+  typeset -g -A _comps
+  autoload -Uz _helmfile
+  _comps[helmfile]=_helmfile
+fi
+
+helmfile completion zsh >| "$ZSH_CACHE_DIR/completions/_helmfile" &|
+
+# Aliases
+alias hf='helmfile'
+alias hfi='helmfile --interactive'