Add minimized export templates

[EthanGrahn]

Summary

As discussed in #50 I've created minimized export templates for each platform. The TEMPLATES.md file includes instructions on how to build new versions when the engine version changes. Each platform has an associated *-custom.py used to define the enabled/disabled features and modules. I've updated export_presets.cfg to use these templates.

Size Comparison

Platform	Default Size (MB)	New Size (MB)
Windows 10 Pro (22H2)	71.5	39.9
Ubuntu 22.04.5	67.6	49.6
MacOS Sonoma 14.5	52.3	47.2

Resolves #50

[MakovWait]

oh thanks! looks pretty interesting! but it is not ok to store the templates via github repo. the best way would be building them during release. so .github/workflows/create-release.yml should be adjusted before we are ready to merge it

[EthanGrahn]

I can remove those files from the pull request. I'm not sure if we'll be able to build the MacOS templates via GitHub actions though, I believe we need them built on Mac hardware. Although I might be mistaken.

Edit: Nevermind! It does appear possible. I'll take a look at this when I get more time.

[EthanGrahn]

I pulled parts of the official Godot workflows to replicate how they create their templates, with a few modifications. This will create the templates and use them for exporting the game, but won't store them in the release. If that's desired I could include that in a separate pull request.