manifests: Move Firefox inclusion to Fedora's manifest

We want to, eventually, remove Firefox from the base image. Before we
can effectively do it, we need to figure out a transition path and make
sure that the Firefox Flatpak is mostly functionally equivalent.

This change does not remove Firefox from the image but moves it to the
Fedora manifest so that downstream builds can exclude it if they want
to.

See: https://gitlab.com/fedora/ostree/sig/-/issues/3
See: https://github.com/fedora-silverblue/issue-tracker/issues/288
See: https://gitlab.com/fedora/sigs/flatpak/fedora-flatpaks/-/issues/13

common: Remove plocate

Remove plocate as this is a command line tool and it comes with a
service that periodically scans the entire filesystem. As we use
containers and Flatpaks, this list of files is not really useful nor
accurate and changes frequently.

We expect users to use graphical tools instead to help them find their
files if needed.

See: https://gitlab.com/fedora/ostree/sig/-/issues/81

common: Add wireguard-tools for all variants

While we expect users to use the support in NetworkManager and
corresponding graphical interfaces to setup WireGuard connections, it is
practical to have the command line tool at hand to validate settings and
debug issues.

Users have also been requesting the additional functionnality provided
by the associated tools and services from the package.

Finally, it is a really small package.

See: https://github.com/fedora-silverblue/issue-tracker/issues/390
See: https://pagure.io/fedora-workstation/issue/353
See: https://pagure.io/fedora-kde/SIG/issue/381

silverblue: Add openssl

While it is not strictly needed for the default installation, it is a
dependency of a frequently installed GNOME Shell extension: GSConnect.

Let's include it as layering is not a great option, containers won't
work here and sysexts are not ready for this yet.

See: https://pagure.io/fedora-workstation/issue/426
See: https://github.com/fedora-silverblue/issue-tracker/issues/201
See: https://github.com/GSConnect/gnome-shell-extension-gsconnect/wiki/Help#openssl-not-found