Add deffile attribute

Summary: The change adds a new attribute `deffile` to the `python_wheel` rule in the `buck2` prelude. This attribute allows specifying a source file for the `deffile`.

Differential Revision: D97208455

fbshipit-source-id: 100d21688402210a902021f804c1ca9d42223e15

Author: Rene van Ee

prelude/python/python_wheel.bzl

@@ -565,6 +565,7 @@ python_wheel = rule(
         rpaths = attrs.list(attrs.string(), default = []),
         lib_dir = attrs.option(attrs.string(), default = None),
         labels = attrs.list(attrs.string(), default = []),
+        deffile = attrs.option(attrs.source(), default = None),
         linker_flags = attrs.list(attrs.arg(anon_target_compatible = True), default = []),
         anonymous_link = attrs.bool(default = True),
         link_execution_preference = link_execution_preference_attr(),