add replacement init script for removed 2021.06 pilot version

versions/2021.06/init/Magic_Castle/bash

@@ -0,0 +1,3 @@
+/cvmfs/pilot.eessi-hpc.org/versions/2021.06/init/print_deprecation_warning.sh
+
+source /cvmfs/pilot.eessi-hpc.org/versions/2021.12/init/Magic_Castle/bash

versions/2021.06/init/bash

@@ -0,0 +1,3 @@
+/cvmfs/pilot.eessi-hpc.org/versions/2021.06/init/print_deprecation_warning.sh
+
+source /cvmfs/pilot.eessi-hpc.org/versions/2021.12/init/bash

versions/2021.06/init/print_deprecation_warning.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+function echo_yellow_stderr() {
+    echo -e "\e[33m${1}\e[0m" >&2
+}
+
+echo_yellow_stderr
+echo_yellow_stderr "WARNING: Version 2021.06 of the EESSI pilot repository has been removed since 16 May 2023."
+echo_yellow_stderr
+echo_yellow_stderr "Version 2021.12 of the EESSI pilot repository can be used as a drop-in replacement, "
+echo_yellow_stderr "so we have prepared your environment to use that instead."
+echo_yellow_stderr
+echo_yellow_stderr "In the future, please run"
+echo_yellow_stderr
+echo_yellow_stderr "    source /cvmfs/pilot.eessi-hpc.org/latest/init/bash"
+echo_yellow_stderr
+echo_yellow_stderr "to prepare your start using the EESSI pilot repository."
+echo_yellow_stderr
+echo_yellow_stderr "See also https://eessi.github.io/docs/using_eessi/setting_up_environment ."
+echo_yellow_stderr