tools/toolbox: Allow to set new toolbox as default for other tools

When specified, write out a small config file that can be sourced
by other scripts to pick the default toolbox container.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2935>

tools/toolbox/create-toolbox.sh

@@ -5,6 +5,7 @@ set -e
 
 TOOLBOX_IMAGE=registry.gitlab.gnome.org/gnome/gnome-shell/toolbox
 DEFAULT_NAME=gnome-shell-devel
+CONFIG_FILE=${XDG_CONFIG_HOME:-$HOME/.config}/gnome-shell-toolbox-tools.conf
 
 usage() {
   cat <<-EOF
@@ -22,6 +23,8 @@ usage() {
 	  -b, --builder           Set up GNOME Builder configuration
 	  --locales=LOCALES       Enable support for additional locales LOCALES
 	  --skip-mutter           Do not build mutter
+	  --set-default           Set as default for other gnome-shell
+	                          toolbox tools
 	  -h, --help              Display this help
 
 	EOF
@@ -76,6 +79,11 @@ setup_classic() {
     https://gitlab.gnome.org/GNOME/gnome-shell-extensions.git $branch
 }
 
+set_default() {
+  mkdir -p $(dirname $CONFIG_FILE)
+  echo DEFAULT_TOOLBOX=$NAME > $CONFIG_FILE
+}
+
 TEMP=$(getopt \
   --name $(basename $0) \
   --options 'n:v:rcbh' \
@@ -86,6 +94,7 @@ TEMP=$(getopt \
   --longoptions 'builder' \
   --longoptions 'locales:' \
   --longoptions 'skip-mutter' \
+  --longoptions 'set-default' \
   --longoptions 'help' \
   -- "$@")
 
@@ -127,6 +136,11 @@ while true; do
       shift
     ;;
 
+    --set-default)
+      SET_DEFAULT=1
+      shift
+    ;;
+
     --locales)
       IFS=" ," LOCALES+=($2)
       shift 2
@@ -161,3 +175,4 @@ install_extra_packages
 
 [[ $SETUP_CLASSIC ]] && setup_classic
 [[ $SETUP_BUILDER ]] && create_builder_config
+[[ $SET_DEFAULT ]] && set_default