getMinGenerationForSeqNo should acquire read lock (#29126)

The method Translog#getMinGenerationForSeqNo does not modify the current
translog but only access, it therefore should acquire the readLock
instead of writeLock.

Author: dnhatn

server/src/main/java/org/elasticsearch/index/translog/Translog.java

@@ -1515,7 +1515,7 @@ public static void writeOperationNoSize(BufferedChecksumStreamOutput out, Transl
      * @return the minimum generation for the sequence number
      */
     public TranslogGeneration getMinGenerationForSeqNo(final long seqNo) {
-        try (ReleasableLock ignored = writeLock.acquire()) {
+        try (ReleasableLock ignored = readLock.acquire()) {
             /*
              * When flushing, the engine will ask the translog for the minimum generation that could contain any sequence number after the
              * local checkpoint. Immediately after flushing, there will be no such generation, so this minimum generation in this case will