Add a graphical environment to releng

I propose evaluating providing a graphical environment with the releng profile.

Pros:

• Graphically configurable keyboard layout selection is easier than doing from the terminal.
• Terminal emulators have scollback unlike the TTY which needs a terminal multiplexer for that. Note: both screen and tmux are included in releng.
• A real web browser is more useful than lynx. E.g. links such as "https://wiki.archlinux.org/title/rfkill" actually work, i.e. the link leads to the exact section as it should instead to the top of the page.
• Potentially allows adding a WebUI installer.
• Easier to connect to Wi-Fi and mobile broadband by using a NetworkManager (#187) frontend. As mentioned in the issue, nmtui is a lot more limited in regards to creating WWAN connections.
• Allows to test if the graphical stack works for a particular hardware before installing Arch on it.

Cons:

• The ISO will be larger.
• Choosing a graphical environment will involve bikeshedding.
• It is unclear if this would improve accessibility or make it worse.

Notes:

• This issue is not about adding any graphical installer.
• Window managers are not an option, since, AFAIK, they all require configuring to be usable. The graphical environment should be usable out of the box.
• @dvzrv wants Wayland instead of Xorg.
• To avoid keyboard layout issues, starting the graphical environment should not require typing. Instead the graphical environment should start on demand by switching the virtual terminal (e.g. to tty5).