Add action to download the source code tar.gz of a GitHub release

[mokagio]

Since moving to XCFramework as the integration method for Gutenberg for Mobile Apps, we have been downloading the source code via Git in order to generate strings, see wordpress-mobile/WordPress-iOS#21416.

Needless to say, checking out the whole repo take a long time, even with --depth 1, which is one of the reasons we moved to XCFramework in the first place.

As we work to hand over release management to the devs, see https://github.com/Automattic/apps-infra-plans/issues/5, it would be good to take the time to remove this bottleneck.

One idea I have is to download the source code from the GitHub release (assuming a release is used, which is in most of the integration cases). After all, what we don't need Git history, only a snapshot of the code.

For reference, the archive for version 1.109.2 is around 20 MB

[mokagio]

I noticed that the GitHub archive doesn't include the Gutenberg submodule, but I think that's okay as neither does the local checkout we currently do. I assume all the strings we need for GMA are defined in the repo itself.

I asked for confirmation, internal ref p1702342331442849-slack-C0126N6JH7Z