Specify the build-system in pyproject.toml (#5531)

### Description

Specify setuptools in the build-system section in pyproject.toml. So
that setuptools gets installed when it is not in the environment when
doing local install.

### Motivation and Context

Fixes #4878

Signed-off-by: Justin Chu <justinchu@microsoft.com>

pyproject.toml

@@ -1,3 +1,7 @@
+[build-system]
+requires = ["setuptools>=61.0.0"]
+build-backend = "setuptools.build_meta"
+
 [tool.mypy]
 follow_imports = "silent"
 strict_optional = true