node-upstream-change([v1.32.2, v1.33.3)): [rocksdb] add metric for num level 0 files (#6791)

## Description

Port
[MystenLabs/sui@262390b](MystenLabs/sui@262390b)

Too many level 0 files can be a trigger to write stall & stop as well

## Links to any relevant issues

Part of #3990

## Type of change

- Enhancement (a non-breaking change which adds functionality)

## How the change has been tested
```
cargo r --bin iota-node -- --config-path fullnode.yaml
```
```
RUST_LOG=info cargo r --bin iota start --force-regenesis --with-faucet
```

Author: gokhan-simsek-iota

crates/typed-store/src/metrics.rs

@@ -84,6 +84,7 @@ pub struct ColumnFamilyMetrics {
     pub rocksdb_total_sst_files_size: IntGaugeVec,
     pub rocksdb_total_blob_files_size: IntGaugeVec,
     pub rocksdb_total_num_files: IntGaugeVec,
+    pub rocksdb_num_level0_files: IntGaugeVec,
     pub rocksdb_current_size_active_mem_tables: IntGaugeVec,
     pub rocksdb_size_all_mem_tables: IntGaugeVec,
     pub rocksdb_num_snapshots: IntGaugeVec,
@@ -130,6 +131,13 @@ impl ColumnFamilyMetrics {
                 registry,
             )
             .unwrap(),
+            rocksdb_num_level0_files: register_int_gauge_vec_with_registry!(
+                "rocksdb_num_level0_files",
+                "Number of level 0 files in the column family",
+                &["cf_name"],
+                registry,
+            )
+            .unwrap(),
             rocksdb_current_size_active_mem_tables: register_int_gauge_vec_with_registry!(
                 "rocksdb_current_size_active_mem_tables",
                 "The current approximate size of active memtable (bytes).",

crates/typed-store/src/rocks/mod.rs

@@ -1034,6 +1034,14 @@ impl<K, V> DBMap<K, V> {
             .rocksdb_total_num_files
             .with_label_values(&[cf_name])
             .set(total_num_files);
+        db_metrics
+            .cf_metrics
+            .rocksdb_num_level0_files
+            .with_label_values(&[cf_name])
+            .set(
+                Self::get_int_property(rocksdb, &cf, &num_files_at_level(0))
+                    .unwrap_or(METRICS_ERROR),
+            );
         db_metrics
             .cf_metrics
             .rocksdb_current_size_active_mem_tables