Nextcloud flatpak can be opened multiple times

It's possible to open multiple instances of the nextcloud flatpak, and all of them attempt to run and sync content at the same time. This may or may not cause consistency issues, so it would be great if the nextcloud flatpak was limited to a single instance running.

Thanks,

Review the linked merged PR #229 and the Flatpak packaging for com.nextcloud.desktopclient.nextcloud first. Confirm that only one instance can run and that concurrent launch attempts do not start another sync process.

Written by the indexing model from the issue text.