[FLINK-9138][docs][tests] Make ConfigOptionsDocsCompletenessTest an IT case

This closes #5975.

flink-docs/pom.xml

@@ -131,6 +131,16 @@ under the License.
 					</execution>
 				</executions>
 			</plugin>
+
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-surefire-plugin</artifactId>
+				<configuration>
+					<systemPropertyVariables>
+						<rootDir>${rootDir}</rootDir>
+					</systemPropertyVariables>
+				</configuration>
+			</plugin>
 		</plugins>
 
 		<pluginManagement>

flink-docs/src/test/java/org/apache/flink/docs/configuration/ConfigOptionsDocsCompletenessITCase.java

@@ -49,7 +49,7 @@ import static org.apache.flink.docs.configuration.ConfigOptionsDocGenerator.stri
  * the same key with different descriptions/default values), and that the documentation does not refer to non-existent
  * options.
  */
-public class ConfigOptionsDocsCompletenessTest {
+public class ConfigOptionsDocsCompletenessITCase {
 
 	@Test
 	public void testDocsCompleteness() throws IOException, ClassNotFoundException {
@@ -99,7 +99,7 @@ public class ConfigOptionsDocsCompletenessTest {
 	}
 
 	private static Map<String, DocumentedOption> parseDocumentedOptions() throws IOException {
-		Path includeFolder = Paths.get("..", "docs", "_includes", "generated").toAbsolutePath();
+		Path includeFolder = Paths.get(System.getProperty("rootDir"), "docs", "_includes", "generated").toAbsolutePath();
 		return Files.list(includeFolder)
 			.filter(path -> path.getFileName().toString().contains("configuration"))
 			.flatMap(file -> {
@@ -145,7 +145,7 @@ public class ConfigOptionsDocsCompletenessTest {
 		Map<String, ExistingOption> existingOptions = new HashMap<>(32);
 
 		for (OptionsClassLocation location : LOCATIONS) {
-			processConfigOptions("..", location.getModule(), location.getPackage(), optionsClass -> {
+			processConfigOptions(System.getProperty("rootDir"), location.getModule(), location.getPackage(), optionsClass -> {
 				List<ConfigOptionsDocGenerator.OptionWithMetaInfo> configOptions = extractConfigOptions(optionsClass);
 				for (ConfigOptionsDocGenerator.OptionWithMetaInfo option : configOptions) {
 					String key = option.option.key();