Merge #5371

5371: Composite embedders r=irevoire a=dureuill

# Pull Request

## Related issue
Fixes #5343 

## What does this PR do?
- Implement [public usage](https://www.notion.so/meilisearch/Composite-embedder-usage-14a4b06b651f81859dc3df21e8cd02a0)
- Refactor the way we check if a parameter is mandatory/allowed/disallowed for a given source
- Take the "nesting context" into account for computer if a parameter is mandatory/allowed/disallowed
- Add tests checking all parameters with all sources, and made sure the results didn't change compared with v1.13

## Dumpless Upgrade

- This adds a new value for an existing parameter => compatible without change
- This adds new optional parameters => compatible without change

Co-authored-by: Louis Dureuil <louis@meilisearch.com>

crates/milli/src/update/new/extract/vectors/mod.rs

@@ -416,7 +416,7 @@ impl<'a, 'b, 'extractor> Chunks<'a, 'b, 'extractor> {
             return Err(crate::Error::UserError(crate::UserError::DocumentEmbeddingError(msg)));
         }
 
-        let res = match embedder.embed_chunks_ref(texts.as_slice(), threads) {
+        let res = match embedder.embed_index_ref(texts.as_slice(), threads) {
             Ok(embeddings) => {
                 for (docid, embedding) in ids.into_iter().zip(embeddings) {
                     sender.set_vector(*docid, embedder_id, embedding).unwrap();