HDFS-17789. Add NormalUnderReplBlocksCount and BadlyDistributedBlocksCount to getStats() NN RPC

[aswinmprabhu]

Description of PR

At LinkedIn, we use the stats from the getStats() NN RPC call to evaluate safety checks that ensure that various maintenance ops are safe to run.

Due to a migration we are undertaking, the badly distributed block count is very high for the cluster undergoing migration. This is not a safety problem. However, to distinguish it from the actual low redundancy block count, we need both these values to be available from the getStats() RPC. The current low redundancy blocks count value available is the sum of all the different types of low redundancy blocks, including normal low redundancy blocks and badly distributed blocks.

This PR adds these 2 values separately to the array returned by getStats() RPC.

How was this patch tested?

Trivial change. It has been running in our prod cluster for a bit now. Build passes:

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  42:50 min
[INFO] Finished at: 2025-05-19T14:51:09+05:30
[INFO] ------------------------------------------------------------------------

For code changes:

• [x] Does the title or this PR starts 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?
• [ ] 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?

[hadoop-yetus]

:broken_heart: -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
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			_ Prechecks _
+1 :green_heart:	dupname	0m 0s		No case conflicting files found.
+0 :ok:	codespell	0m 1s		codespell was not available.
+0 :ok:	detsecrets	0m 1s		detect-secrets was not available.
+1 :green_heart:	@author	0m 0s		The patch does not contain any @author tags.
-1 :x:	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 _
+0 :ok:	mvndep	6m 3s		Maven dependency ordering for branch
+1 :green_heart:	mvninstall	20m 3s		trunk passed
+1 :green_heart:	compile	3m 8s		trunk passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 :green_heart:	compile	2m 51s		trunk passed with JDK Private Build-1.8.0_452-8u452-ga~us1-0ubuntu1~20.04-b09
+1 :green_heart:	checkstyle	0m 47s		trunk passed
+1 :green_heart:	mvnsite	1m 29s		trunk passed
+1 :green_heart:	javadoc	1m 13s		trunk passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 :green_heart:	javadoc	1m 51s		trunk passed with JDK Private Build-1.8.0_452-8u452-ga~us1-0ubuntu1~20.04-b09
+1 :green_heart:	spotbugs	3m 19s		trunk passed
+1 :green_heart:	shadedclient	21m 51s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+0 :ok:	mvndep	0m 22s		Maven dependency ordering for patch
+1 :green_heart:	mvninstall	1m 6s		the patch passed
+1 :green_heart:	compile	3m 14s		the patch passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 :green_heart:	javac	3m 14s		the patch passed
+1 :green_heart:	compile	2m 59s		the patch passed with JDK Private Build-1.8.0_452-8u452-ga~us1-0ubuntu1~20.04-b09
+1 :green_heart:	javac	2m 59s		the patch passed
+1 :green_heart:	blanks	0m 0s		The patch has no blanks issues.
-0 :warning:	checkstyle	0m 42s	/results-checkstyle-hadoop-hdfs-project.txt	hadoop-hdfs-project: The patch generated 1 new + 169 unchanged - 0 fixed = 170 total (was 169)
+1 :green_heart:	mvnsite	1m 14s		the patch passed
-1 :x:	javadoc	0m 25s	/results-javadoc-javadoc-hadoop-hdfs-project_hadoop-hdfs-client-jdkUbuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04.txt	hadoop-hdfs-project_hadoop-hdfs-client-jdkUbuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04 with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04 generated 4 new + 1161 unchanged - 0 fixed = 1165 total (was 1161)
+1 :green_heart:	javadoc	1m 28s		the patch passed with JDK Private Build-1.8.0_452-8u452-ga~us1-0ubuntu1~20.04-b09
+1 :green_heart:	spotbugs	3m 13s		the patch passed
+1 :green_heart:	shadedclient	23m 53s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 :green_heart:	unit	2m 9s		hadoop-hdfs-client in the patch passed.
+1 :green_heart:	unit	11m 5s		hadoop-hdfs in the patch passed.
+1 :green_heart:	asflicense	0m 22s		The patch does not generate ASF License warnings.
		115m 59s

Subsystem	Report/Notes
Docker	ClientAPI=1.49 ServerAPI=1.49 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-7695/1/artifact/out/Dockerfile
GITHUB PR	https://github.com/apache/hadoop/pull/7695
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
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Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-7695/1/testReport/
Max. process+thread count	1158 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs-client hadoop-hdfs-project/hadoop-hdfs U: hadoop-hdfs-project
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-7695/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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