Add gradle tasks related to zipping sample projects

[devloglogan]

@m4gr3d mentioned that having the vendor repo's sample projects available on the asset library would be super handy for users of the XR Editor. I think it makes most sense to host the zips of these in the vendor repo releases. This PR adds some gradle tasks to generate/clean those.

I'll add the zipped projects to the 3.0.1 release if we agree on this approach.

[devloglogan]

Fixed the zipSamples task to also include the root directory in the zip, rather than just the contents. I've attached zips of the samples to the 3.0.1 release.

[dsnopek]

Thanks!

For the most part, this looks good.

However, taking a peek at the ZIP files that were added to the release, they included the android/ directory, which shouldn't be included. That should be added by the version of Godot that the user has, and not be bundled with the project.

It'd be great if the gradle task could omit that directory? That way, we don't have to be careful about not including it.

[devloglogan]

However, taking a peek at the ZIP files that were added to the release, they included the android/ directory, which shouldn't be included. That should be added by the version of Godot that the user has, and not be bundled with the project.

Ah, my mistake! Just updated the PR so the task removes those directories as well. Will update the release zips. Thanks!

[m4gr3d]

Looks good!

[dsnopek]

Thanks, looks good!