Customize the alarm sound

Recently I got an email with a feature request for Clocks. Probably due to having done the most recent commit at the time. Since I am not really involved with Clocks myself I am gonna repost it here and unsub from the notifications.

Email content:

Greetings from Costa Rica,

Hoping you can point me in the right direction.
I have the app installed on a 18.04LTS system but the tone of the alarm is too high a frequency for me to hear. Probably because of my age.
Could you possibly tell me how I might be able to configure Clocks so that I can adjust the frequency of the alarm tone to something I can hear? I picked your email address because I saw it at the gitlab site which was a bit too complex for me.
I sure would be nice if I could play a mp3 file as my alarm.

Thanks for reading my email.

Dennis,

Regards