Introduce Index::unique_index_with_prefix(&str)

It could be used when we want to see the index name in the assertions,
e.g. `movies-[uuid]`

Signed-off-by: Martin Tzvetanov Grigorov <mgrigorov@apache.org>

crates/meilisearch/tests/common/server.rs

@@ -347,6 +347,16 @@ impl<State> Server<State> {
         }
     }
 
+    pub fn unique_index_with_prefix(&self, prefix: &str) -> Index<'_> {
+        let uuid = Uuid::new_v4();
+        Index {
+            uid: format!("{prefix}-{}", uuid.to_string()),
+            service: &self.service,
+            encoder: Encoder::Plain,
+            marker: PhantomData,
+        }
+    }
+
     pub fn unique_index_with_encoder(&self, encoder: Encoder) -> Index<'_> {
         let uuid = Uuid::new_v4();
         Index { uid: uuid.to_string(), service: &self.service, encoder, marker: PhantomData }