feat: add metrics for region server (#2552)

* feat: add metircs for region server

* fix: add comment and remove unused code

src/store-api/src/region_request.rs

@@ -43,6 +43,23 @@ pub enum RegionRequest {
 }
 
 impl RegionRequest {
+    /// Returns the type name of the [RegionRequest].
+    #[inline]
+    pub fn request_type(&self) -> &'static str {
+        match &self {
+            RegionRequest::Put(_) => "put",
+            RegionRequest::Delete(_) => "delete",
+            RegionRequest::Create(_) => "create",
+            RegionRequest::Drop(_) => "drop",
+            RegionRequest::Open(_) => "open",
+            RegionRequest::Close(_) => "close",
+            RegionRequest::Alter(_) => "alter",
+            RegionRequest::Flush(_) => "flush",
+            RegionRequest::Compact(_) => "compact",
+            RegionRequest::Truncate(_) => "truncate",
+        }
+    }
+
     /// Convert [Body](region_request::Body) to a group of [RegionRequest] with region id.
     /// Inserts/Deletes request might become multiple requests. Others are one-to-one.
     pub fn try_from_request_body(body: region_request::Body) -> Result<Vec<(RegionId, Self)>> {