Merge #3851

3851: Expose lastUpdate and isIndexing in /stats endpoint r=dureuill a=gentcys

# Pull Request

## Related issue
Fixes #3843

## What does this PR do?
- expose lastUpdate in `/stats` endpoint
- expose isIndex in `stats` endpoint
- add a method `is_task_processing` in index-scheduler/src/lib.rs.

## 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: Cong Chen <cong.chen@ocrlabs.com>
Co-authored-by: ManyTheFish <many@meilisearch.com>
Co-authored-by: Louis Dureuil <louis@meilisearch.com>

index-scheduler/src/lib.rs

@@ -807,6 +807,11 @@ impl IndexScheduler {
         Ok(res)
     }
 
+    // Return true if there is at least one task that is processing.
+    pub fn is_task_processing(&self) -> Result<bool> {
+        Ok(!self.processing_tasks.read().unwrap().processing.is_empty())
+    }
+
     /// Return true iff there is at least one task associated with this index
     /// that is processing.
     pub fn is_index_processing(&self, index: &str) -> Result<bool> {
@@ -1833,6 +1838,17 @@ mod tests {
         snapshot!(snapshot_index_scheduler(&index_scheduler), name: "registered_the_third_task");
     }
 
+    #[test]
+    fn test_task_is_processing() {
+        let (index_scheduler, mut handle) = IndexScheduler::test(true, vec![]);
+
+        index_scheduler.register(index_creation_task("index_a", "id")).unwrap();
+        snapshot!(snapshot_index_scheduler(&index_scheduler), name: "registered_a_task");
+
+        handle.advance_till([Start, BatchCreated]);
+        assert!(index_scheduler.is_task_processing().unwrap());
+    }
+
     /// We send a lot of tasks but notify the tasks scheduler only once as
     /// we send them very fast, we must make sure that they are all processed.
     #[test]