feat(hasura): add completion plugin (#11278)

plugins/hasura/README.md

+# Hasura plugin
+
+This plugin adds completion for [the Hasura CLI](https://hasura.io/docs/latest/hasura-cli/index/).
+
+To use it, add `hasura` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... hasura)
+```

plugins/hasura/hasura.plugin.zsh

+if (( ! $+commands[hasura] )); then
+  return
+fi
+
+# If the completion file does not exist, generate it and then source it
+# Otherwise, source it and regenerate in the background
+if [[ ! -f "$ZSH_CACHE_DIR/completions/_hasura" ]]; then
+  hasura completion zsh --file "$ZSH_CACHE_DIR/completions/_hasura" >/dev/null
+  source "$ZSH_CACHE_DIR/completions/_hasura"
+else
+  source "$ZSH_CACHE_DIR/completions/_hasura"
+  hasura completion zsh --file "$ZSH_CACHE_DIR/completions/_hasura" >/dev/null &|
+fi