[Enhancement]: Use bundled runner GStreamer

[chriskempson]

Describe the bug

If I choose a runner, 'GE Wine' for example, I'd expect my application to make use of GE Wine's bundled GStreamer.

Steam achieves this when running Proton GE by setting an environment variable akin to GST_PLUGIN_SYSTEM_PATH=/home/user/.var/app/com.usebottles.bottles/data/bottles/runners/wine-ge-7-28

To Reproduce

N/A

Package

Flatpak from Flathub

Distribution

N/A

Troubleshooting Logs

None

Display Protocol

No response

Display Backend used by Bottles

No response

Additional context

No response