Demonstrate Dense Vectors and KNN as part of the Films example

Considering that Solr 9.0 introduced Dense Vectors and KNN, it would be good to have these features demonstrated in a builtin example.

The idea would be to add a new Dense Vector field in the existing films dataset that would be a vector representation of the films. Then, we could add some example KNN queries showing the multiple ways that vectors could be used with Solr.

I already have an initial separated example in a personal fork of mine, I plan to work on merging it with the current existing films example.

The idea for this issue rised in discussion with epugh in another issue related to KNN and Dense Vectors (SOLR-16567).