feat: support dedicated server builds

[paulpach]

Changes

• Add modules for dedicated server build

should fix game-ci/documentation#240

Checklist

• Read the contribution guide and accept the code of conduct
• Readme (updated or not needed)

[github-actions]

[webbertakken]

Hi @paulpach,

This looks good overall.

It would be nice to know how much these additional build target modules add to the images. If it is a lot we might opt to make separate images for these. Hopefully we can go with your solution though.

Could you please verify that the resulting images in fact work as expected when building a project?

[paulpach]

Might be worth separating:

[webbertakken]

Might be worth separating

Perhaps. Although for Linux and Windows it's quite acceptable it seems.

Do server builds require IL2CPP or not? If yes, then that will not be supported in docker, as MacOS images currently do not exist as per macoscontainers.org. In that case we can simply support Windows and Linux with docker and MacOS like we already do in unity-builder (game-ci/unity-builder#326)

[paulpach]

It does not look like it. I was able to build a mono dedicated server.

So should I remove the mac support and just leave linux and windows server support? maybe separate them in 3 prs?

Honestly I only care about linux servers, I added the other ones for consistency.

[webbertakken]

I'm also doubtful about how common the usecase of MacOS server really is.

Perhaps the right course of action here is to see the actual difference in disk space of the image builds for Linux and Windows (base target module vs. both base and server target module) - could you please post these based on image builds?. If the difference is within 5% we might just go forward with this, without MacOS server support in a first iteration.

What do you think?

[paulpach]

These are the sizes in GB of the docker images obtained by the 'docker images' command
"Player only" is what you have today.
"Player + Server" is the images with this PR.
"Server only" is an image with only the server module. I do not know if this is enough to do a build. I will test that tomorrow.

Platform	Player only	Player + Server	Server only
Linux	6.94	7.38 (+6.3%)	6.59
Windows	7.94	9.71 (+22.2%)	7.94
Mac	8.03	11.7 (+45.7%)	9.85

I only care about Linux server. I reckon someone might care about windows server, probably not as often though. I would be surprised if anyone ever asks you for mac server support.

[webbertakken]

Despite the % increase I'm thinking lets include Linux Server and Windows Server as targets on their respective platforms and leave MacOS Server out of this entirely.

WDYT @GabLeRoux @davidmfinol @frostebite?

[davidmfinol]

Agreed with moving forward with just Linux and Windows servers.

I'd also be surprised if anyone ever asked for Mac server.

[davidmfinol]

If we do move forward with Linux and Windows servers as targets, would they include IL2CPP?
We've identified that IL2CPP is not necessarily required, as people can do mono server builds.
However, I imagine that some users would want IL2CPP server builds?

[webbertakken]

Looks great! Thank you very much.