[Tooling] Add automation lane to fetch translations

[iangmaia]

Fixes AINFRA-1036

Description

This PR adds the lane download_translations that will fetch the translations from the Gravatar iOS GlotPress project and add them to the Xcode project.

I've also ran the lane for the first time to initially add the files (though I noticed the only language with actual translations was Swedish, just like Android).

Testing Steps

1. Checkout this branch
2. Add translations to one of the GlotPress projects mentioned above
3. Run bundle exec download_translations skip_commit:true
4. Verify that the added translation has been correctly downloaded to the project.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Gravatar Prototype Build by scanning the QR code below to install the corresponding build.

	App Name	Gravatar Prototype Build
	Build Number	443
	Version	PR #96
	Bundle ID	com.gravatar.GravatarApp.prototype
	Commit	02fefd2
	Installation URL	2pfl60ah9p6oo

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