Respect .gitattributes archiving rules when copying files to match asset store releases

[Tattomoosa]

In https://docs.godotengine.org/en/stable/community/asset_library/submitting_to_assetlib.html it's recommended to modify .gitattributes for addons submitted to the asset store to only include the addons folder, like so:

# .gitattributes

# Addon store download only includes addons folder
/**        export-ignore
/addons    !export-ignore
/addons/** !export-ignore

It should either be an optional behavior or (imo preferably) the default behavior to respect the plugin's provided archiving rules when copying files. This would fix at least one issue initially installing a repo structured in a somewhat nonstandard way (https://github.com/anthonyec/godot_little_camera_preview/tree/main - it has a separate project file stored at res://demo with its own addons folder, which adds res://demo to the project root after matching on the internal addons folder)

If it was the default behavior, it would mean that gd-plug would almost always provide the exact same release as the asset library