Merge #5232

5232: Stabilize vector store feature r=Kerollmops a=dureuill

# Pull Request

## Related issue
Fixes #4733 

## What does this PR do?
- `vectorStore` feature can no longer be set or get from `/experimental-features`
- That feature has been removed, and there is no longer any check for its activation
- Always display `embedders` in the settings, even if empty
- Always hide `_vectors` in documents, unless `retrieveVectors: true`
- Make error codes consistent with the usual nomenclature
- Update tests as needed


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

crates/milli/src/error.rs

@@ -222,7 +222,9 @@ and can not be more than 511 bytes.", .document_id.to_string()
     #[error("Too many embedders in the configuration. Found {0}, but limited to 256.")]
     TooManyEmbedders(usize),
     #[error("Cannot find embedder with name `{0}`.")]
-    InvalidEmbedder(String),
+    InvalidSearchEmbedder(String),
+    #[error("Cannot find embedder with name `{0}`.")]
+    InvalidSimilarEmbedder(String),
     #[error("Too many vectors for document with id {0}: found {1}, but limited to 256.")]
     TooManyVectors(String, usize),
     #[error("`.embedders.{embedder_name}`: Field `{field}` unavailable for source `{source_}` (only available for sources: {}). Available fields: {}",

crates/milli/src/search/new/vector_sort.rs

@@ -32,7 +32,7 @@ impl<Q: RankingRuleQueryTrait> VectorSort<Q> {
             .index
             .embedder_category_id
             .get(ctx.txn, embedder_name)?
-            .ok_or_else(|| crate::UserError::InvalidEmbedder(embedder_name.to_owned()))?;
+            .ok_or_else(|| crate::UserError::InvalidSearchEmbedder(embedder_name.to_owned()))?;
 
         Ok(Self {
             query: None,

crates/milli/src/search/similar.rs

@@ -65,10 +65,9 @@ impl<'a> Similar<'a> {
         let universe = universe;
 
         let embedder_index =
-            self.index
-                .embedder_category_id
-                .get(self.rtxn, &self.embedder_name)?
-                .ok_or_else(|| crate::UserError::InvalidEmbedder(self.embedder_name.to_owned()))?;
+            self.index.embedder_category_id.get(self.rtxn, &self.embedder_name)?.ok_or_else(
+                || crate::UserError::InvalidSimilarEmbedder(self.embedder_name.to_owned()),
+            )?;
 
         let reader = ArroyWrapper::new(self.index.vector_arroy, embedder_index, self.quantized);
         let results = reader.nns_by_item(