Add musify

Adds Musify.

• rfp#2379 (closed)
• https://github.com/gokadzev/Musify/discussions/165

Required

• The app complies with the inclusion criteria — ✔ Includes an updater, see linked discussion below
• The original app author has been notified (and does not oppose the inclusion) — https://github.com/gokadzev/Musify/discussions/165
• All related fdroiddata and RFP issues have been referenced in this merge request
• Builds with fdroid build

Strongly Recommended

• The upstream app source code repo contains the app metadata (summary/description/images/changelog/etc) in a Fastlane or Triple-T folder structure
• Releases are tagged

Suggested

• External repos are added as git submodules instead of srclibs
• Enable Reproducible Builds
• Multiple apks for native code

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Closes rfp#2379 (closed)