Implement automatic download and pull request creation for fully translated content from Crowdin

[jordangriffiths01]

When translation of a markdown file on Crowdin is completed, this should automatically be retrieved and included in a pull request to the develop branch for review.

Although Crowdin ships with GitHub integration, this is not suitable for our use case. We want to selectively include translations once they are available. The included GitHub integration seems more designed for cases where all translation occurs before a deployment, and so it includes ALL translated files (including non/partially translated files which still contain source strings) in pull requests it makes.

Currently, the only mechanism to be notified of a completed translation is via a webhook. This would require a server running on some platform to receive the notification (via an HTTP request), download the translated file, and open a pull request.