Spotify Tray Icon Support

### Specifications
- Hardcode-Tray version : `4.3`
- Distribution : `Fedora 38`
- Gtk version : `3.24`
- Application name : `Spotify`
- Application version : `1.2.20.1210.g2a8a8a57`
- KDE Plasma Version: `5.27.7`
- KDE Frameworks Version: `5.109.0`
- Qt Version: `5.15.10`
- Kernel Version: `6.4.15-200.fc38.x86_64 (64-bit)`
- Icon pack: [papirus-icon-theme](https://github.com/PapirusDevelopmentTeam/papirus-icon-theme)

Just recently Spotify updated the app to version 1.2.20 and it now uses [libayatana-appindicator](https://copr.fedorainfracloud.org/coprs/till/xpad/packages/). Out of the box the app now supports minimizing to tray.


Papirus icon pack supports spotify indicator:


You can install spotify client from:
https://negativo17.org/spotify-client/
https://github.com/negativo17/spotify-client

Or snap:
https://snapcraft.io/spotify `sudo snap install spotify --edge`

Start by locating the existing Spotify and tray-icon handling, then trace the code path that recognizes application indicators such as libayatana-appindicator. Compare it with the behavior described for Spotify 1.2.20. Done means Spotify's tray indicator is handled correctly by Hardcode-Tray and existing behavior remains intact.

Written by the indexing model from the issue text.