HDFS-17971. Fix RAT check failure for vendored JSON.java in hadoop-hdfs-rbf.

[slfan1989]

Description of PR

HDFS-17971. Fix RAT check failure for vendored JSON.java in hadoop-hdfs-rbf.

The Apache RAT check fails in the hadoop-hdfs-rbf module
because src/main/java/org/apache/hadoop/hdfs/server/federation/metrics/JSON.java
is reported as an unapproved license file.

This class was copied from Jetty and intentionally retains its original dual EPL/Apache license header. It is already documented in LICENSE.txt and excluded from the root-level RAT check.
However, hadoop-hdfs-rbf defines its own RAT exclusion list, which did not include this file.

This patch adds JSON.java to the module-level RAT exclusion list. It does not modify the source file or its original license header.

This is a follow-up to HADOOP-19951 and #8654.

How was this patch tested?

The failure was reproduced before applying the patch:

Unapproved: 1, unknown: 1
BUILD FAILURE

The following command was run after applying the patch:

./mvnw -pl hadoop-hdfs-project/hadoop-hdfs-rbf \
  -DskipTests apache-rat:check

Result:

Unapproved: 0, unknown: 0
BUILD SUCCESS

For code changes:

• Does the title of this PR start with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: Have the integration tests been executed and the endpoint
  declared according to the connector-specific documentation? Note: Automated CI
  testing doesn't cover all cases so manual testing with cloud storage is still
  required.
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

AI Tooling

If an AI tool was used:

• The PR includes the phrase "Contains content generated by "
  where is the name of the AI tool used.
• My use of AI contributions follows the ASF legal policy
  https://www.apache.org/legal/generative-tooling.html

[slfan1989]

@zhtttylz Could you please help review this PR? Thank you very much!

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 21s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+0 🆗	detsecrets	0m 1s		detect-secrets was not available.
+0 🆗	xmllint	0m 1s		xmllint was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
-1 ❌	test4tests	0m 0s		The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
			_ trunk Compile Tests _
+1 💚	mvninstall	26m 32s		trunk passed
+1 💚	compile	0m 41s		trunk passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	compile	0m 53s		trunk passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
+1 💚	mvnsite	0m 51s		trunk passed
+1 💚	javadoc	0m 40s		trunk passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	javadoc	0m 40s		trunk passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
+1 💚	shadedclient	46m 25s		branch has no errors when building and testing our client artifacts.
-0 ⚠️	patch	46m 41s		Used diff version of patch file. Binary files and potentially other changes not applied. Please rebase and squash commits if necessary.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 31s		the patch passed
+1 💚	compile	0m 24s		the patch passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	javac	0m 24s		the patch passed
+1 💚	compile	0m 33s		the patch passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
+1 💚	javac	0m 33s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	mvnsite	0m 34s		the patch passed
+1 💚	javadoc	0m 21s		the patch passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	javadoc	0m 20s		the patch passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
+1 💚	shadedclient	16m 36s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	37m 59s		hadoop-hdfs-rbf in the patch passed.
+1 💚	asflicense	0m 25s		The patch does not generate ASF License warnings.
		105m 20s

Subsystem	Report/Notes
Docker	ClientAPI=1.55 ServerAPI=1.55 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8708/1/artifact/out/Dockerfile
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient codespell detsecrets xmllint
uname	Linux 477d100bf0b8 5.15.0-190-generic #200-Ubuntu SMP Fri Aug 7 15:06:04 UTC 2026 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / c48027a
Default Java	Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
Multi-JDK versions	/usr/lib/jvm/java-21-openjdk-amd64:Ubuntu-21.0.11+10-1-24.04.2-Ubuntu /usr/lib/jvm/java-17-openjdk-amd64:Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8708/1/testReport/
Max. process+thread count	3995 (vs. ulimit of 10000)
modules	C: hadoop-hdfs-project/hadoop-hdfs-rbf U: hadoop-hdfs-project/hadoop-hdfs-rbf
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8708/1/console
versions	git=2.43.0 maven=3.9.15
Powered by	Apache Yetus 0.14.1 https://yetus.apache.org

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[zhtttylz]

LGTM. +1.

[slfan1989]

@zhtttylz Thanks for the review!