Merge #5355

5355: Support fetching the pooling method from the model configuration r=Kerollmops a=dureuill

# Pull Request

## Related issue
Fixes #5354 

## What does this PR do?
- Fetches the pooling configuration from the model repository
- Use a pooling method that depends on the pooling configuration of that model.
- Allow overriding the pooling method with a new huggingFace embedder parameter `pooling`
  - for backward-compatibility with Meilisearch v1.13
  - for compatibility with embedders that exhibit the same behavior as Meilisearch v1.13
- Handle the default value of that new parameter
   - for compatibility, when importing a db/a dump, it should be set to `forceMean`
   - when (re)set from the settings for an embedder, it should be set to `useModel`


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

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

@@ -2768,6 +2768,7 @@ mod tests {
                         source: Setting::Set(crate::vector::settings::EmbedderSource::UserProvided),
                         model: Setting::NotSet,
                         revision: Setting::NotSet,
+                        pooling: Setting::NotSet,
                         api_key: Setting::NotSet,
                         dimensions: Setting::Set(3),
                         document_template: Setting::NotSet,