Nextcloud Tray Icon missing on Gnome Wayland sessions

I was testing the nextcloud-client flatpak in Fedora SilverBlue 32.

I noticed that on the Wayland session I was not seeing the nextcloud tray icon. My system has installed the `gnome-shell-extension-appindicator` as a layered package to help facilitate this. I also tested the [element flatpak](https://github.com/flathub/im.riot.Riot/) that had a working tray icon. Comparing the settings from element and that I was getting a system tray icon in a Gnome on Xorg session I was able to resolve this by adding the `socket=fallback-x11` permission.

More over I noticed from element's settings that only `org.kde.StatusNotifierItem-2-1=own` was needed instead if `org.kde.*=own` for the indicator to show up.

Here are some information from my set up for reproducibility of the results.

```
$ flatpak info --show-permissions com.nextcloud.desktopclient.nextcloud
[Context]
shared=network;ipc;
sockets=x11;wayland;fallback-x11;
devices=dri;
filesystems=xdg-run/Nextcloud:create;xdg-config/kdeglobals:ro;host;

[Session Bus Policy]
org.kde.StatusNotifierWatcher=talk
com.canonical.AppMenu.Registrar=talk
org.freedesktop.Notifications=talk
org.freedesktop.secrets=talk
org.kde.StatusNotifierItem-2-1=own

[Environment]
TMPDIR=/var/tmp
$ flatpak info --show-permissions im.riot.Riot
[Context]
shared=network;ipc;
sockets=x11;pulseaudio;
devices=all;
filesystems=xdg-download;xdg-run/keyring;

[Session Bus Policy]
org.kde.StatusNotifierWatcher=talk
org.freedesktop.portal.Fcitx=talk
org.freedesktop.Notifications=talk
org.kde.StatusNotifierItem-2-1=own
$ echo $XDG_SESSION_TYPE
wayland
$ cat /etc/os-release
NAME=Fedora
VERSION="32.20200912.0 (Silverblue)"
ID=fedora
VERSION_ID=32
VERSION_CODENAME=""
PLATFORM_ID="platform:f32"
PRETTY_NAME="Fedora 32.20200912.0 (Silverblue)"
ANSI_COLOR="0;34"
LOGO=fedora-logo-icon
CPE_NAME="cpe:/o:fedoraproject:fedora:32"
HOME_URL="https://fedoraproject.org/"
DOCUMENTATION_URL="https://docs.fedoraproject.org/en-US/fedora-silverblue/"
SUPPORT_URL="https://fedoraproject.org/wiki/Communicating_and_getting_help"
BUG_REPORT_URL="https://bugzilla.redhat.com/"
REDHAT_BUGZILLA_PRODUCT="Fedora"
REDHAT_BUGZILLA_PRODUCT_VERSION=32
REDHAT_SUPPORT_PRODUCT="Fedora"
REDHAT_SUPPORT_PRODUCT_VERSION=32
PRIVACY_POLICY_URL="https://fedoraproject.org/wiki/Legal:PrivacyPolicy"
VARIANT="Silverblue"
VARIANT_ID=silverblue
OSTREE_VERSION='32.20200912.0'
$ rpm-ostree status
State: idle
Deployments:
● ostree://fedora:fedora/32/x86_64/silverblue
Version: 32.20200912.0 (2020-09-12T16:13:20Z)
BaseCommit: 8dc4fb5bb5d63db1791aa1027af328c036fc7f1ed6bfb5c28cc0667d73ce9de7
GPGSignature: Valid signature by 97A1AE57C3A2372CCA3A4ABA6C13026D12C944D0
LayeredPackages: fedora-workstation-repositories gnome-shell-extension-appindicator gnome-shell-extension-dash-to-dock pam-u2f pamu2fcfg

```

P.S.1: [Flatseal](https://github.com/flathub/com.github.tchx84.Flatseal) was an awesome software to help me look into this.
P.S.2: Happy to make a PR for this if maintainer(s) are willing to implement those changes.