Generate command to build pylibcudf (#375)

This makes the build-pylibcudf-python command and makes build-cudf
depend on it.

Potentially needs admin-merge when changes look good?
cc @vyasr

---------

Co-authored-by: Paul Taylor <178183+trxcllnt@users.noreply.github.com>

features/src/rapids-build-utils/opt/rapids-build-utils/manifest.yaml

@@ -78,6 +78,10 @@ repos:
  sub_dir: cpp/libcudf_kafka
  depends: [cudf]
  python:
+ - name: pylibcudf
+ sub_dir: python/pylibcudf
+ depends: [cudf]
+ args: {cmake: -DFIND_CUDF_CPP=ON, install: *rapids_build_backend_args}
  - name: cudf
  sub_dir: python/cudf
  depends: [cudf]