Fix Open-in-Slack on KDE

Slack use a magic URL like slack://T08PSQ7BQ/magic-login/<magic-id> to open a workspace on Slack Desktop.

On KDE, here is a bug: https://bugs.kde.org/show_bug.cgi?id=429408#c3

It looks like this:

kde-open slack://T08PSQ7BQ/magic-login/<magic-id>

but kde-open turn it to:

slack -s slack://t08psq7bq/magic-login/<magic-id>
                 ^ --- lowercase workspace id

A bypass way to resolve it is create /usr/local/bin/xdg-open with following content:

#!/usr/bin/env bash
 
if [[ "${1:-}" = slack://* ]]; then
    exec /usr/lib/slack/slack --enable-crashpad "$1"
fi
 
exec /usr/bin/xdg-open "$@"

Reference: https://stackoverflow.com/a/71579300/9018019