chore: Add crate licenses. (#4158)

- GPUI and all dependencies: Apache 2
- Everything else: AGPL

Here's a script that I've generated for it:
https://gist.github.com/osiewicz/6afdd6626e517da24a2092807e6f0b6e

Release Notes:
- N/A

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Co-authored-by: David <david@zed.dev>