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/index_documents/extract/extract_vector_points.rs

@@ -795,7 +795,7 @@ fn embed_chunks(
     unused_vectors_distribution: &UnusedVectorsDistribution,
     request_threads: &ThreadPoolNoAbort,
 ) -> Result<Vec<Vec<Embedding>>> {
-    match embedder.embed_chunks(text_chunks, request_threads) {
+    match embedder.embed_index(text_chunks, request_threads) {
         Ok(chunks) => Ok(chunks),
         Err(error) => {
             if let FaultSource::Bug = error.fault {

crates/milli/src/update/index_documents/mod.rs

@@ -2778,6 +2778,8 @@ mod tests {
                         response: Setting::NotSet,
                         distribution: Setting::NotSet,
                         headers: Setting::NotSet,
+                        search_embedder: Setting::NotSet,
+                        indexing_embedder: Setting::NotSet,
                         binary_quantized: Setting::NotSet,
                     }),
                 );