Include license in project metadata

I'd completely forgotten to specify it before, other than in the 
project classifiers. This meant that the license file wasn't included
in the sdist or wheels, and *that* was causing the conda-forge
builds to fail.

pyproject.toml

@@ -1,9 +1,10 @@
 [project]
-version = "0.3.0"
+version = "0.4.0"
 name = "odc-loader"
 description = "Tooling for constructing xarray objects from parsed metadata"
 readme = "README.md"
 requires-python = ">= 3.10"
+license = {file = "LICENSE"}
 dependencies = [
     "affine",
     "odc-geo>=0.4.7",