HDFS-17950. Add FedBalance operational control switches

[qijiale76]

Description of PR

Large FedBalance jobs may need operator-controlled stop and resume points, especially around the initial copy, incremental copy, and final cutover window.

This issue proposes adding optional operational control switches for FedBalance. All new controls are disabled by default and do not change the existing default behavior.

Proposed controls:

• Stop after the initial DistCp succeeds.
• Start a later job from the incremental DistCp stage after validating the required prior-copy state.
• Stop instead of retrying forever when the diff is small enough but final-copy conditions are blocked by open files.
• Gate leaving the incremental DistCp stage on a time-window sentinel path.
• Allow a sentinel path to make open files force-closeable.

These controls make long-running FedBalance migrations easier to operate while preserving the current default behavior.

How was this patch tested?

Ran FedBalance unit tests locally and validated on a production cluster.

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[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	18m 26s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 1s		No case conflicting files found.
+0 🆗	codespell	0m 0s		codespell was not available.
+0 🆗	detsecrets	0m 0s		detect-secrets was not available.
+0 🆗	xmllint	0m 0s		xmllint was not available.
+0 🆗	markdownlint	0m 0s		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.
			_ trunk Compile Tests _
+0 🆗	mvndep	2m 19s		Maven dependency ordering for branch
+1 💚	mvninstall	52m 13s		trunk passed
+1 💚	compile	18m 3s		trunk passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	compile	18m 19s		trunk passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
+1 💚	checkstyle	5m 58s		trunk passed
+1 💚	mvnsite	2m 33s		trunk passed
+1 💚	javadoc	1m 51s		trunk passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	javadoc	1m 47s		trunk passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
-1 ❌	spotbugs	1m 5s	/branch-spotbugs-hadoop-tools_hadoop-federation-balance-warnings.html	hadoop-tools/hadoop-federation-balance in trunk has 12 extant spotbugs warnings.
+1 💚	shadedclient	34m 39s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+0 🆗	mvndep	0m 27s		Maven dependency ordering for patch
+1 💚	mvninstall	1m 31s		the patch passed
+1 💚	compile	16m 46s		the patch passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	javac	16m 46s		the patch passed
+1 💚	compile	18m 19s		the patch passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
+1 💚	javac	18m 19s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	5m 55s		the patch passed
+1 💚	mvnsite	2m 32s		the patch passed
+1 💚	javadoc	1m 48s		the patch passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	javadoc	1m 42s		the patch passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
+1 💚	spotbugs	4m 0s		the patch passed
+1 💚	shadedclient	36m 8s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	3m 9s		hadoop-federation-balance in the patch passed.
+1 💚	unit	48m 37s		hadoop-hdfs-rbf in the patch passed.
+1 💚	asflicense	1m 15s		The patch does not generate ASF License warnings.
		310m 32s

Subsystem	Report/Notes
Docker	ClientAPI=1.55 ServerAPI=1.55 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8583/1/artifact/out/Dockerfile
GITHUB PR	#8583
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets xmllint markdownlint
uname	Linux 18e017de2e7a 5.15.0-181-generic #191-Ubuntu SMP Fri May 22 19:09:02 UTC 2026 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / 9d251db
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-8583/1/testReport/
Max. process+thread count	4620 (vs. ulimit of 10000)
modules	C: hadoop-tools/hadoop-federation-balance hadoop-hdfs-project/hadoop-hdfs-rbf U: .
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8583/1/console
versions	git=2.43.0 maven=3.9.15 spotbugs=4.9.7
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