[BUG] incorrect distance metric formula for innerproduct in knn scriptscoring

[tstadel]

What is the bug?
The formula for the innerproduct distance measure equals the l1 distance metric, not dotproduct. If I get it correctly, innerproduct in scriptscoring is fully supported and correctly uses the dotproduct formula as distance metric (see this PR in opendistro). So this formula should be corrected in order to avoid confusion. Otherwise (if it's actually calculating l1 for innerproduct space_type) there should be an explanation why this is the case.

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Go to knn scriptscoring docs
2. Scroll down to the distance metric table
3. See error for innerproduct row.

What is the expected behavior?
Innerproduct formula should equal the dotproduct formula.