Include LICENSE file in wheel metadata

[daniel7an]

Adds LICENSE to the include list in pyproject.toml so the license file is included in wheel distributions.

Fixes #3965

[aytekinar]

I believe this is the wrong approach. LICENSE does exist in the wheel distribution; however, its License-File metadata is missing somehow.

I would leave include as before, and instead, add license-files = ["LICENSE"] right below the license key of [project].