HDFS-16547: Backported feature to dissallow observer transition if namenode is in safemode

[adityarverma]

Description of PR

This PR backports a feature #4201.
Origin patch JIRA: HDFS-16547.

Currently, when a Namenode is in safemode(under starting or enter safemode manually), we can transfer this Namenode to Observer by command. This Observer node may receive many requests and then throw a SafemodeException, this causes unnecessary failover on the client.
Also, When a new Block Token is made by namenode it is not propagated to the datanodes if namenode is in safemode, all requests going to the observer namenode start failing with "Block token verification failed" error.

So Namenode in safe mode should not be transfer to observer state.

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	10m 28s		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.
+0 🆗	markdownlint	0m 1s		markdownlint was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s		The patch appears to include 2 new or modified test files.
			_ branch-3.3 Compile Tests _
+1 💚	mvninstall	49m 10s		branch-3.3 passed
+1 💚	compile	1m 14s		branch-3.3 passed
+1 💚	checkstyle	0m 54s		branch-3.3 passed
+1 💚	mvnsite	1m 20s		branch-3.3 passed
+1 💚	javadoc	1m 33s		branch-3.3 passed
+1 💚	spotbugs	3m 13s		branch-3.3 passed
+1 💚	shadedclient	41m 5s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	1m 15s		the patch passed
+1 💚	compile	1m 5s		the patch passed
+1 💚	javac	1m 5s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	0m 42s		the patch passed
+1 💚	mvnsite	1m 12s		the patch passed
+1 💚	javadoc	1m 21s		the patch passed
+1 💚	spotbugs	3m 8s		the patch passed
+1 💚	shadedclient	40m 16s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
-1 ❌	unit	235m 40s	/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch passed.
+1 💚	asflicense	0m 44s		The patch does not generate ASF License warnings.
		392m 4s

Reason	Tests
Failed junit tests	hadoop.hdfs.server.datanode.TestLargeBlockReport
	hadoop.hdfs.protocol.TestBlockListAsLongs
	hadoop.hdfs.qjournal.client.TestQJMWithFaults
	hadoop.hdfs.TestDFSInotifyEventInputStreamKerberized
	hadoop.hdfs.server.balancer.TestBalancerWithHANameNodes

Subsystem	Report/Notes
Docker	ClientAPI=1.47 ServerAPI=1.47 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-7321/1/artifact/out/Dockerfile
GITHUB PR	#7321
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets xmllint markdownlint
uname	Linux e5a0dbebced0 5.15.0-125-generic #135-Ubuntu SMP Fri Sep 27 13:53:58 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	branch-3.3 / 349acbd
Default Java	Private Build-1.8.0_362-8u372-gaus1-0ubuntu118.04-b09
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-7321/1/testReport/
Max. process+thread count	2174 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs U: hadoop-hdfs-project/hadoop-hdfs
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-7321/1/console
versions	git=2.17.1 maven=3.6.0 spotbugs=4.2.2
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