Chore: remove setup.py in favor of pyproject.toml for custom materializations example (#4514)

Author: georgesittas

examples/custom_materializations/pyproject.toml

@@ -1,3 +1,16 @@
 [build-system]
 requires = ["setuptools >= 61.0", "setuptools_scm"]
 build-backend = "setuptools.build_meta"
+
+[project]
+name = "custom_materializations"
+requires-python = ">=3.9"
+version = "0.1.0"
+dependencies = ["sqlmesh"]
+
+[project.entry-points."sqlmesh.materializations"]
+custom_full_materialization = "custom_materializations.full:CustomFullMaterialization"
+custom_full_with_custom_kind = "custom_materializations.custom_kind:CustomFullWithCustomKindMaterialization"
+
+[tool.setuptools.packages.find]
+include = ["custom_materializations"]