feat(plugins): add grc plugin for Generic Colouriser (#9315)

Co-authored-by: Marc Cornellà <marc.cornella@live.com>

plugins/grc/README.md

+# Generic Colouriser plugin
+
+This plugin adds wrappers for commands supported by [Generic Colouriser](https://github.com/garabik/grc):
+
+To use it, add `grc` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... grc)
+```
+
+## Commands
+
+The following commands are wrapped by `grc` so that their output is automatically colored:
+
+- `cc`
+- `configure`
+- `cvs`
+- `df`
+- `diff`
+- `dig`
+- `gcc`
+- `gmake`
+- `ifconfig`
+- `iwconfig`
+- `last`
+- `ldap`
+- `make`
+- `mount`
+- `mtr`
+- `netstat`
+- `ping`
+- `ping6`
+- `ps`
+- `traceroute`
+- `traceroute6`
+- `wdiff`
+- `whois`

plugins/grc/grc.plugin.zsh

+# Adapted from: https://github.com/garabik/grc/blob/master/grc.zsh
+
+if [[ "$TERM" = dumb ]] || (( ! $+commands[grc] )); then
+  return
+fi
+
+# Supported commands
+cmds=(
+  cc
+  configure
+  cvs
+  df
+  diff
+  dig
+  gcc
+  gmake
+  ifconfig
+  iwconfig
+  last
+  ldap
+  make
+  mount
+  mtr
+  netstat
+  ping
+  ping6
+  ps
+  traceroute
+  traceroute6
+  wdiff
+  whois
+)
+
+# Set alias for supported commands
+for cmd in $cmds; do
+  if (( $+commands[$cmd] )); then
+    eval "function $cmd {
+      grc --colour=auto \"${commands[$cmd]}\" \"\$@\"
+    }"
+  fi
+done
+
+# Clean up variables
+unset cmds cmd