Allow setting custom sound for Timers

[Starcr0ss]

Describe your suggested feature

Similar to the AOSP app, allow users to set a custom timer sound when it expires. Because this app provides the (better) functionality of seeing a list of running timers, maybe you can implement custom sounds per timer along with a default one. The global custom sound is more than enough, but it just seems like it would be possible to add the feature of per-timer alert setting.

Other details

No response

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