Add reloadable flag to gdextension file

[paddy-exe]

adds the reloadable flag to the .gdextension file for quickly getting started and having the extension be reloadable almost from the get-go

[Ivorforce]

Should probably test that this works, but LGTM

[dsnopek]

LGMT!

[van800]

Hi all! What is the reason for this to default to false?
The doc has it true. https://docs.godotengine.org/en/4.6/tutorials/scripting/cpp/gdextension_cpp_example.html

[dsnopek]

The inclusion in the template is intended as an example, so folks know it's there and can easily change it.

Using reloadable=true is only really appropriate for when GDExtension is used to script your game (as opposed to making a reusable extension), which is the use-case that is being shown in the docs linked above.

Also, there's a godot-cpp option that needs to be enable for reload to work, although it's currently enabled by default. And not all extensions are safe to be reloaded - in particular, if your extension includes an editor plugin, special care needs to be taken when reloading.