[state-sync] version counters

Prefer this model of type safety and simplicity... so introducing it
here where I have more work to do...

state-synchronizer/src/coordinator.rs

@@ -455,12 +455,8 @@ impl<T: ExecutorProxyTrait> SyncCoordinator<T> {
         let synced_version = self.local_state.highest_version_in_local_storage();
         let committed_version = self.local_state.highest_local_li.ledger_info().version();
         let local_epoch = self.local_state.epoch();
-        counters::VERSION
-            .with_label_values(&[counters::SYNCED_VERSION_LABEL])
-            .set(synced_version as i64);
-        counters::VERSION
-            .with_label_values(&[counters::COMMITTED_VERSION_LABEL])
-            .set(committed_version as i64);
+        counters::set_version(counters::VersionType::Synced, synced_version);
+        counters::set_version(counters::VersionType::Committed, committed_version);
         counters::EPOCH.set(local_epoch as i64);
         debug!(LogSchema::new(LogEntry::LocalState)
             .local_li_version(committed_version)

state-synchronizer/src/counters.rs

@@ -19,9 +19,30 @@ pub const CHUNK_REQUEST_MSG_LABEL: &str = "chunk_request";
 pub const CHUNK_RESPONSE_MSG_LABEL: &str = "chunk_response";
 
 // version type labels
-pub const COMMITTED_VERSION_LABEL: &str = "committed"; // Version of latest ledger info committed.
-pub const SYNCED_VERSION_LABEL: &str = "synced"; // Version of most recent txn that was synced (even if it is not backed by an LI)
-pub const TARGET_VERSION_LABEL: &str = "target"; // Version a node is trying to catch up to
+pub fn set_version(version_type: VersionType, version: u64) {
+    VERSION
+        .with_label_values(&[version_type.as_str()])
+        .set(version as i64)
+}
+
+pub enum VersionType {
+    /// Version of latest ledger info committed.
+    Committed,
+    /// Version of most recent txn that was synced (even if it is not backed by an LI)
+    Synced,
+    /// Current version a node is trying to catch up to usually within the current epoch
+    Target,
+}
+
+impl VersionType {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            VersionType::Committed => "committed",
+            VersionType::Synced => "synced",
+            VersionType::Target => "target",
+        }
+    }
+}
 
 // failed channel send type labels
 pub const CONSENSUS_SYNC_REQ_CALLBACK: &str = "consensus_sync_req_callback";

state-synchronizer/src/request_manager.rs

@@ -318,9 +318,7 @@ impl RequestManager {
         // TODO set target version of chunk request in counter
         if failed_peer_sends.is_empty() {
             if let Some(version) = target_version {
-                counters::VERSION
-                    .with_label_values(&[counters::TARGET_VERSION_LABEL])
-                    .set(version as i64);
+                counters::set_version(counters::VersionType::Target, version);
             }
             Ok(())
         } else {