feat(logcli): add completion plugin (#14158)

plugins/logcli/README.md

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+# logcli plugin
+
+This plugin adds completion for [Grafana Loki's logcli](https://grafana.com/docs/loki/latest/query/logcli/).
+
+To use it, add `logcli` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... logcli)
+```
+
+This plugin does not add any aliases.
+
+## Cache
+
+This plugin caches the completion script and automatically updates it when the
+plugin is loaded, which is usually when you start a new terminal emulator.
+
+The cache is stored at `$ZSH_CACHE_DIR/completions/_logcli`.

plugins/logcli/logcli.plugin.zsh

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+# Autocompletion for Grafana Loki's CLI (logcli).
+if (( ! $+commands[logcli] )); then
+  return
+fi
+
+# If the completion file doesn't exist yet, we need to autoload it and
+# bind it to `logcli`. Otherwise, compinit will have already done that.
+if [[ ! -f "$ZSH_CACHE_DIR/completions/_logcli" ]]; then
+  typeset -g -A _comps
+  autoload -Uz _logcli
+  _comps[logcli]=_logcli
+fi
+
+zmodload -F zsh/files b:zf_mv
+() {
+  local TMPPREFIX="$ZSH_CACHE_DIR/completions/._logcli"
+  zf_mv -f -- =( logcli --completion-script-zsh ) "$ZSH_CACHE_DIR/completions/_logcli"
+} &|