Added MicroK8s plugin for ZSH (#8499)

* Added MicroK8s plugin for ZSH

* Added caching for kubectl and helm commands

* Added title in compadd and enhanced README

plugins/microk8s/README.md

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+# MicroK8s plugin
+
+This plugin provides completion and useful aliases for [MicroK8s](https://microk8s.io/).
+
+To use it, add `microk8s` to the plugins array in your zshrc file.
+
+```zsh
+plugins=(... microk8s)
+```
+
+## Aliases
+
+| Alias | Command          | Description                                                                                              |
+|-------|------------------|----------------------------------------------------------------------------------------------------------|
+| mco   | microk8s.config  | Shows the Kubernetes config file.                                                                        |
+| mct   | microk8s.ctr     | Interact with containerd CLI.                                                                            |
+| mdi   | microk8s.disable | Disables an addon.                                                                                       |
+| me    | microk8s.enable  | Enables an addon.                                                                                        |
+| mh    | microk8s.helm    | Interact with Helm CLI.                                                                                  |
+| mis   | microk8s.istio   | Interact with Istio CLI.                                                                                 |
+| mk    | microk8s.kubectl | Interact with Kubernetes CLI.                                                                            |
+| msp   | microk8s.stop    | Stops all Kubernetes services.                                                                           |
+| mst   | microk8s.start   | Starts MicroK8s after it is being stopped.                                                               |
+| msts  | microk8s.status  | Provides an overview of the MicroK8s state (running / not running) as well as the set of enabled addons. |

plugins/microk8s/microk8s.plugin.zsh

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+# ---------------------------------------------------------- #
+# Aliases and Completions for MicroK8s (https://microk8s.io) #
+# Author: Shaun Tabone (https://github.com/xontab)           #
+# ---------------------------------------------------------- #
+
+# Helper function to cache and load completions
+_microk8s_cache_completion() {
+  local cache="${ZSH_CACHE_DIR}/microk8s_$(echo $1)_completion"
+  if [[ ! -f $cache ]]; then
+    $2 $cache
+  fi
+
+  [[ -f $cache ]] && source $cache
+}
+
+# ---------------------------------------------------------- #
+# microk8s.enable                                            #
+# ALIAS: me                                                  #
+# ---------------------------------------------------------- #
+_microk8s_enable_get_command_list() {
+  microk8s.enable --help | tail -n +7 | awk '{$1=$1;print}'
+}
+
+_microk8s_enable() {
+   compadd -X "MicroK8s Addons" $(_microk8s_enable_get_command_list)
+}
+
+compdef _microk8s_enable microk8s.enable
+alias me='microk8s.enable'
+
+# ---------------------------------------------------------- #
+# microk8s.disable                                           #
+# ALIAS: mdi                                                 #
+# ---------------------------------------------------------- #
+_microk8s_disable_get_command_list() {
+  microk8s.disable --help | tail -n +7 | awk '{$1=$1;print}'
+}
+
+_microk8s_disable() {
+  compadd -X "MicroK8s Addons" $(_microk8s_disable_get_command_list)
+}
+
+compdef _microk8s_disable microk8s.disable
+alias mdi='microk8s.disable'
+
+# ---------------------------------------------------------- #
+# microk8s.kubectl                                           #
+# ALIAS: mk                                                  #
+# ---------------------------------------------------------- #
+_microk8s_kubectl_completion() {
+  if [ $commands[microk8s.kubectl] ]; then
+    microk8s.kubectl 2>/dev/null >/dev/null && microk8s.kubectl completion zsh | sed 's/__start_kubectl kubectl/__start_kubectl microk8s.kubectl/g' >$1
+  fi
+}
+
+_microk8s_cache_completion 'kubectl' _microk8s_kubectl_completion
+
+alias mk='microk8s.kubectl'
+
+# ---------------------------------------------------------- #
+# microk8s.helm                                              #
+# ALIAS: mh                                                  #
+# ---------------------------------------------------------- #
+_microk8s_helm_completion() {
+  if [ $commands[microk8s.helm] ]; then
+    microk8s.helm completion zsh | sed 's/__start_helm helm/__start_helm microk8s.helm/g' >$1
+  fi
+}
+
+_microk8s_cache_completion 'helm' _microk8s_helm_completion
+
+alias mh='microk8s.helm'
+
+# ---------------------------------------------------------- #
+# Other Aliases                                              #
+# ---------------------------------------------------------- #
+alias mco='microk8s.config'
+alias mct='microk8s.ctr'
+alias mis='microk8s.istio'
+alias mst='microk8s.start'
+alias msts='microk8s.status'
+alias msp='microk8s.stop'