vendoring: split sync and update make targets
vendoring: split sync and update make targets

The sync target previously regenerated the poetry.lock for vendored
packages, causing larger than necessary change set for patches. This
change introduces the update target to specifically handle lock file
updates, lock target to regenerate the lock file and repurpose the sync
target to only sync as expected.

python-poetry/poetry-core,python-poetry/poetry-core,python-poetry/poetry-core