Consider Making Drake an Optional Dependency

[AlexandreAmice]

In the pyproject.toml drake is mandatory dependency.

This can lead to an issue where two versions of Drake must be installed if someone may want to use the manipulation repository, but use a locally built version of Drake.

Is it worth marking this dependency as optional?

[nepfaff]

Making it an optional dependency seems a bit weird to me as the code doesn't run without Drake. A better option might be to add the custom Drake version to PYTHONPATH. This takes precedence over pip packages and is how I used to handle this case.

[RussTedrake]

strongly agree. or one can install drake into the venv via the build process.