Add a rule to expand jinja2 templates to a file. BUG=b:262458659 TEST=portage/tools/run_tests.sh Change-Id: Ia76f595e57910e6b66f834b9f199ab8edbe826e2 Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/bazel/+/5367139 Auto-Submit: Matt Stark <msta@google.com> Commit-Queue: Matt Stark <msta@google.com> Reviewed-by: Tim Bain <tbain@google.com> Tested-by: Matt Stark <msta@google.com>