Add support for XDG Background portal

[OlivierM16]

Description

Pika Backup can not run in background to run schedulings.

-- Bug reported on Solus packages github previously : --

xdg-desktop-portal-xapp actually does seem to support it at least partially, but that would require wiring up support in Budgie.

Anyway, since this is a Budgie-specific issue with regards to them needing to implement Background portal support somehow and not a packaging issue I'm going to go ahead and close this one. I recommend you make an issue over in the Budgie repo if one does not already exist.

--

Budgie version

budgie-desktop 10.9.2

Operating System

Solus 4.6 convergence

Steps to reproduce the issue

1. Run Pika Backup (flatpak)
2. Try to activate schedule functionnality
3. Pika Backup show an alert about xdg-desktop-portal

Actual result

Pika does not work in background, no schedule possible.

Expected result

Pika Backup running in background to activate schedulings.

Additional information

There's some information about this issue here :
https://world.pages.gitlab.gnome.org/pika-backup/help/C/feature-schedule.html

Troubleshooting
Pika Backup uses the xdg-desktop-portal Background Portal to configure the Monitor process to run in the background. Some distributions misconfigure xdg-desktop-portal or don't enable the Background Portal. This will then cause an error when enabling scheduled backups. We have tested the following distributions for correct behavior regarding background portals in their stock configuration:

• Debian

• Fedora

If you encounter issues with enabling scheduled backups and you are using a different distribution, please report an issue in your distribution issue tracker.