chg: [rsync-backup-target] use color when outputing diff when available

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

rsync-backup-target/resources/bin/compose-add-rsync-key

@@ -125,8 +125,11 @@ EOF
         exit 1
     fi
     echo "${WHITE}Applying these changes:${NORMAL}"
-    echo "$diff"
-
+    if type -p colordiff >/dev/null; then
+        colordiff -u "$compose_file" <(echo "$content")
+    else
+        echo "$diff"
+    fi | egrep -v "^[^ ]*(---|\+\+\+)"
     cp "$compose_file" "${compose_file}.old"
     echo "$content" > "$compose_file"