Sample Godot game packaging

Hi,

Following the thread at [1] I noticed we don't have a sample Godot 
package for new contributors to copy^Wstudy from. I went ahead and wrote 
an initial package for Godot's tutorial game "Dodge the Creeps!":

https://salsa.debian.org/games-team/dodge-the-creeps

It takes the source repository and generates an arch-independent Debian 
package with a .pck file for godot3-runner, as well as system menu and 
software center entries. It took longer than I thought, so I expect this 
will come in handy :)

I want this to be a collegial effort, so please test, review and write 
suggestions. This is about newcomer-friendly packaging -- let's aim at 
simplicity and keep pet peeves [2] under control ;)

Cheers!
Sylvain

[1] https://lists.debian.org/debian-devel-games/2021/02/msg00004.html
[2] https://en.wikipedia.org/wiki/Wikipedia:No_pet_peeve_wars