[notifications] feat: add custom notification sound files plugin (#12782)

* add config plugin for notification sounds

* add sound test android

* add ios sound test

* lint plugin

* docs

[notifications] feat: add custom notification sound files plugin (#12782)

* add config plugin for notification sounds

* add sound test android

* add ios sound test

* lint plugin

* docs

* update readme

* changelog

* move functions to be tested into it. statements

* feedback on NotificationsPluginProps

* remove fs-extra, move some methods from async to sync

* fix argument order

* address iOS feedback

* update docs and readme

* lint

* add plugin to ncl

* add test to NCL

* account for breaking change in @expo/config-plugins

* set isBuildFile: true

* re yarn after rebase

* lint

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