SNOW-928802 Use concurrent hashmap to prevent ConcurrentModificationE…

…xception

- We did make a change to use ConcurrentHashMap but that was in test
  code, we still used HashMap! This will hopefully not result into
  ConcurrentModificationException

src/main/java/net/snowflake/ingest/streaming/internal/FlushService.java

@@ -174,7 +174,7 @@ List<List<ChannelData<T>>> getData() {
     this.isNeedFlush = false;
     this.lastFlushTime = System.currentTimeMillis();
     this.isTestMode = isTestMode;
-    this.latencyTimerContextMap = new HashMap<>();
+    this.latencyTimerContextMap = new ConcurrentHashMap<>();
     this.bdecVersion = this.owningClient.getParameterProvider().getBlobFormatVersion();
     createWorkers();
   }