Merge #4787

4787: Add index exists function in index_scheduler which stops opening indexes to only check if they exist. r=Kerollmops a=Karribalu

# Pull Request

## Related issue
Fixes #4784

## What does this PR do?
- Added index_exists function in the index_scheduler.
- Resolved opening indexes to only check if they exist.
- Made changes to existing tests to test this function.

## PR checklist
Please check if your PR fulfills the following requirements:
- [x] Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
- [x] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Thank you so much for contributing to Meilisearch!


Co-authored-by: karribalu <karri.balu123456@gmail.com>

index-scheduler/src/lib.rs

@@ -662,7 +662,11 @@ impl IndexScheduler {
         let rtxn = self.env.read_txn()?;
         self.index_mapper.index(&rtxn, name)
     }
-
+    /// Return the boolean referring if index exists.
+    pub fn index_exists(&self, name: &str) -> Result<bool> {
+        let rtxn = self.env.read_txn()?;
+        self.index_mapper.index_exists(&rtxn, name)
+    }
     /// Return the name of all indexes without opening them.
     pub fn index_names(&self) -> Result<Vec<String>> {
         let rtxn = self.env.read_txn()?;
@@ -3795,15 +3799,15 @@ mod tests {
         ]);
         snapshot!(snapshot_index_scheduler(&index_scheduler), name: "after_processing_the_10_tasks");
 
-        // The index should not exists.
-        snapshot!(format!("{}", index_scheduler.index("doggos").map(|_| ()).unwrap_err()), @"Index `doggos` not found.");
+        // The index should not exist.
+        snapshot!(matches!(index_scheduler.index_exists("doggos"), Ok(true)), @"false");
     }
 
     #[test]
     fn test_document_addition_cant_create_index_without_index_without_autobatching() {
         // We're going to execute multiple document addition that don't have
         // the right to create an index while there is no index currently.
-        // Since the autobatching is disabled, every tasks should be processed
+        // Since the auto-batching is disabled, every task should be processed
         // sequentially and throw an IndexDoesNotExists.
         let (index_scheduler, mut handle) = IndexScheduler::test(false, vec![]);
 
@@ -3845,8 +3849,8 @@ mod tests {
         handle.advance_n_failed_batches(5);
         snapshot!(snapshot_index_scheduler(&index_scheduler), name: "all_tasks_processed");
 
-        // The index should not exists.
-        snapshot!(format!("{}", index_scheduler.index("doggos").map(|_| ()).unwrap_err()), @"Index `doggos` not found.");
+        // The index should not exist.
+        snapshot!(matches!(index_scheduler.index_exists("doggos"), Ok(true)), @"false");
     }
 
     #[test]