Add flatpak extension path also for Convolver and RNNoise

[Digitalone1]

@vchernin This is related to this issue.

Please test it.

I wonder if it's better to use /app/extensions/easyeffects-presets. Maybe Presets is too generic? Could /app/extensions path be used also by other Flatpak apps?

[github-actions]

Workflow failed, but the following artifacts are still available for this pull request:

• easyeffects-archlinux-merge-fb3972a06-into-7d1e5cf40-x86_64.zip
• easyeffects-flatpak-merge-fb3972a06-into-7d1e5cf40-x86_64.zip

[vchernin]

I wonder if it's better to use /app/extensions/easyeffects-presets. Maybe Presets is too generic? Could /app/extensions path be used also by other Flatpak apps?

The current /app/extensions/Presets should not be a problem. The reason these presets are able to install at extensions/Presets is because we have defined it here:

easyeffects/util/flatpak/com.github.wwmm.easyeffects.Devel.json

Line 31 in 35b69a7

"directory": "extensions/Presets",

What other flatpak apps or extensions are doing cannot conflict with that directory without us modifying that file. For example the audio plugins are sometimes using extensions/Plugins but that is fine since they can only use that directory currently.