[FLINK-22510][core] Format durations with highest unit

When converting a configuration value to a string, durations were formatted
in nanoseconds regardless of their values. This produces serialized outputs
which are hard to understand for humans.

The functionality of formatting in the highest unit which allows the value
to be an integer already exists, thus we can simply defer to it to produce
a more useful result.

Author: Airblader

flink-core/src/main/java/org/apache/flink/configuration/ConfigurationUtils.java

@@ -389,7 +389,7 @@ static String convertToString(Object o) {
             return (String) o;
         } else if (o.getClass() == Duration.class) {
             Duration duration = (Duration) o;
-            return String.format("%d ns", duration.toNanos());
+            return TimeUtils.formatWithHighestUnit(duration);
         } else if (o instanceof List) {
             return ((List<?>) o)
                     .stream()

flink-core/src/test/java/org/apache/flink/configuration/ConfigurationTest.java

@@ -340,8 +340,7 @@ public void testToMap() {
 
         assertEquals(listValues, configuration.toMap().get(listConfigOption.key()));
         assertEquals(mapValues, configuration.toMap().get(mapConfigOption.key()));
-        assertEquals(
-                duration.toNanos() + " ns", configuration.toMap().get(durationConfigOption.key()));
+        assertEquals("3 s", configuration.toMap().get(durationConfigOption.key()));
     }
 
     enum TestEnum {

flink-core/src/test/java/org/apache/flink/configuration/ConfigurationUtilsTest.java

@@ -22,13 +22,17 @@
 
 import org.junit.Test;
 
+import java.time.Duration;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Properties;
 
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertThat;
 
 /** Tests for the {@link ConfigurationUtils}. */
@@ -92,4 +96,29 @@ public void testGetPrefixedKeyValuePairs() {
 
         assertThat(resultKeyValuePairs, is(equalTo(expectedKeyValuePairs)));
     }
+
+    @Test
+    public void testConvertToString() {
+        // String
+        assertEquals("Simple String", ConfigurationUtils.convertToString("Simple String"));
+
+        // Duration
+        assertEquals("0 ms", ConfigurationUtils.convertToString(Duration.ZERO));
+        assertEquals("123 ms", ConfigurationUtils.convertToString(Duration.ofMillis(123L)));
+        assertEquals("1234 s", ConfigurationUtils.convertToString(Duration.ofMillis(1_234_000L)));
+        assertEquals("25 h", ConfigurationUtils.convertToString(Duration.ofHours(25L)));
+
+        // List
+        final List<Object> listElements = new ArrayList<>();
+        listElements.add("Test;String");
+        listElements.add(Duration.ZERO);
+        listElements.add(42);
+        assertEquals("'Test;String';0 ms;42", ConfigurationUtils.convertToString(listElements));
+
+        // Map
+        final Map<Object, Object> mapElements = new HashMap<>();
+        mapElements.put("A:,B", "C:,D");
+        mapElements.put(10, 20);
+        assertEquals("'''A:,B'':''C:,D''',10:20", ConfigurationUtils.convertToString(mapElements));
+    }
 }

flink-table/flink-sql-client/src/test/java/org/apache/flink/table/client/config/YamlConfigUtilsTest.java

@@ -112,8 +112,8 @@ public void testExecutionEntryToConfigOption() throws Exception {
                         "parallelism.default=1",
                         "pipeline.auto-watermark-interval=99",
                         "pipeline.max-parallelism=16",
-                        "restart-strategy.failure-rate.delay=1000000000 ns",
-                        "restart-strategy.failure-rate.failure-rate-interval=99000000000 ns",
+                        "restart-strategy.failure-rate.delay=1 s",
+                        "restart-strategy.failure-rate.failure-rate-interval=99 s",
                         "restart-strategy.failure-rate.max-failures-per-interval=10",
                         "restart-strategy.fixed-delay.delay=1000",
                         "restart-strategy=failure-rate",