minetest: Provide default gameid argument

Since Minetest 5.8.0, there is no longer a "default" game, so the --gameid argument must be used to select a game (from the list at https://content.luanti.org/packages/?type=game).

Set minetest_game as the default game for FreedomBox. In the future, we can consider providing a list of popular game IDs, or allow a custom game ID.

Work around for Debian bug #1090067.

Closes: #2445 (closed).

Tests:

• Install Minetest on Debian testing. The service is running. Able to connect a client to the server.

Signed-off-by: James Valleroy jvalleroy@mailbox.org