feat(sift-benchmark): use l2 squared dist for weaviate

[etiennedi]

closes #360

Assumes #359 was already merged. I did not rebase this on the other branch or merge the other one in here, as I want to leave this to you. This will not create any conflicts, but at the same time the feature won't be used if the changes from #359 are not presetn.

Goals:

• [x] use l2 distance in sift benchmark for Weaviate
• [x] check and update documentation, if required. See guide