Add optional dependencies to the universal_hub

[aignas]

Whilst thinking about #3594, I realized that it would be good to add dependencies if they are present, but not fail if they are not present.

API that would be good:

    deps = [
        "@pypi//must",
    ] + select({
        "@pypi//optional:is_present": ["@pypi//optional"],
        "//conditions:default": [],
    }),