[SPARK-28248][SQL][TEST] Upgrade docker image and library for PostgreSQL integration test

## What changes were proposed in this pull request?

This pr upgrades Postgres docker image for integration tests.

## How was this patch tested?

manual tests:
```
./build/mvn install -DskipTests
./build/mvn test -Pdocker-integration-tests -pl :spark-docker-integration-tests_2.12
```

Closes apache#25050 from wangyum/SPARK-28248.

Authored-by: Yuming Wang <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: wangyum

external/docker-integration-tests/src/test/scala/org/apache/spark/sql/jdbc/PostgresIntegrationSuite.scala

@@ -29,7 +29,7 @@ import org.apache.spark.tags.DockerTest
 @DockerTest
 class PostgresIntegrationSuite extends DockerJDBCIntegrationSuite {
   override val db = new DatabaseOnDocker {
-    override val imageName = "postgres:9.4.5"
+    override val imageName = "postgres:11.4"
     override val env = Map(
       "POSTGRES_PASSWORD" -> "rootpass"
     )

pom.xml

@@ -896,7 +896,7 @@
       <dependency>
         <groupId>org.postgresql</groupId>
         <artifactId>postgresql</artifactId>
-        <version>9.4.1207.jre7</version>
+        <version>42.2.6</version>
         <scope>test</scope>
       </dependency>
       <dependency>