Secrets Portal support

https://flatpak.github.io/xdg-desktop-portal/docs/doc-org.freedesktop.portal.Secret.html

The latest dev version of Qtcord won't work because it can't access the system keyring. It uses the keyring library to handle storing secrets, but it doesn't have support for libportal.

Start with the linked Secret portal documentation and inspect the existing keyring integration in Qtcord. Identify the entry point where secrets are stored and determine how libportal support should fit there; done means the latest development version can access the system keyring through the Secrets portal.

Written by the indexing model from the issue text.