Update LICENSE and add LICENSE_HEADER

[davidberenstein1957]

We got this comment on X https://twitter.com/ImageDeeply/status/1743982093707710835
I copied the license file from https://github.com/argilla-io/argilla/edit/develop/LICENSE, which seems to work properly in the Argilla repo.

[alvarobartt]

Fair, thanks! This would be a breaking change, since we inject the LICENSE on top of each file, could you create a LICENSE_HEADER with the previous stuff, and then change the path within .pre-commit-config.yaml so that's injected instead of LICENSE?