DOPS-602: Change how mmctl gets packaged and locally fetched. (#18335)

* DOPS-602: Change how mmctl gets packaged and locally fetched.

scripts/mmctl-dev.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -xe
+
+if [[ "$(basename "$PWD")" != "mattermost-server" ]]; then
+  echo "please run this script from the root project folder of mattermost-server with ./scripts/mmctl-dev.sh"
+  exit 1
+fi
+
+if [ ! -d "../mmctl" ]; then
+  echo "please clone mmctl as a companion repository on the same level next to mattermost-server (git@github.com:mattermost/mmctl.git)"
+  exit 1
+fi
+
+cd ../mmctl
+make build
+cd -
+
+cp ../mmctl/mmctl bin/mmctl
+
+./bin/mmctl version