Setup CI

[GeekCornerGH]

Hi, I may make a PR to implement CI, just tell me what you'd like the CI to do @Alexejhero

[Alexejhero]

CI steps should look like this:

On push to main or develop or PR to main or develop

• Clone the repo
• Restore nuget packages
• Build the mod in debug and attach the file as an artifact
• Build the mod in release and attach the file as an artifact

If the action was triggered by push to main, also do the following:

• Find the latest DRAFT release in the repo, if there is none, abort
• Attach the release dll to the draft release, overriding old files if they exist
• Download the external dependencies (BepInEx, Reactor) from a build data file
• Setup an appropriate folder structure including the dependencies and the built mod
• Zip up the result and attach it to the draft release as well, overriding old files if they exist

There's no build data file in the repo yet, but I imagine it would look something like this:

{
    "build": {
        "path": "BepInEx/plugins"
    },
    "dependencies": {
        "BepInEx": {
            "download": "https://builds.bepinex.dev/projects/bepinex_be/688/BepInEx-Unity.IL2CPP-win-x86-6.0.0-be.688%2B4901521.zip",
            "path": ".",
            "unarchive": true
        },
        "Reactor": {
            "download": "https://github.com/NuclearPowered/Reactor/releases/download/2.2.0/Reactor.dll",
            "path": "BepInEx/plugins"
        }
    }
}

Copying the mod dll to build.path can be hardcoded, as in we don't have to worry about multiple csprojects because Submerged is and will always be compiled down to a single DLL, so it's enough to copy the release dll to whatever the path says.

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Since the unity assetbundle file is committed in the repo for now, I left out any CI steps for the unity project, that can be figured out later (I'm not even sure if there should be CI or not for it)