Add 'sort' filter to specify results order

[JackSwingle01]

Added sort filter based on https://blog.gdeltproject.org/gdelt-doc-2-0-api-debuts/

[alex9smith]

Hey @JackSwingle01 thanks for the PR and sorry it's taken me a while to get to it.

I'm trying to slowly move any validation logic out of the Filters class to stop it being so unwieldy. Are you able to move your new static method to a separate function in validation.py? It'd be great to see some simple tests for it like the validate_tone function has too. You'll also need to rebase onto the latest main.

I'm happy to pick up those changes too if you want to give me write permission to your branch.