[fix](Nereids) Fix add BE with properties return UnsupportedOperationException err (#50163)

…Exception err

due to https://github.com/apache/doris/pull/47951

sql `ALTER SYSTEM ADD BACKEND "175.42.51.1:9050" PROPERTIES
("tag.compute_group_name" = "another_compute_group");`

```
Caused by: java.lang.UnsupportedOperationException
        at com.google.common.collect.UnmodifiableIterator.remove(UnmodifiableIterator.java:50) ~[guava-33.2.1-jre.jar:?]
        at org.apache.doris.common.util.PropertyAnalyzer.analyzeBackendTagsProperties(PropertyAnalyzer.java:1350) ~[doris-fe.jar:1.2-SNAPSHOT]
        at org.apache.doris.nereids.trees.plans.commands.info.AddBackendOp.validate(AddBackendOp.java:45) ~[doris-fe.jar:1.2-SNAPSHOT]
        at org.apache.doris.nereids.trees.plans.commands.AlterSystemCommand.validate(AlterSystemCommand.java:90) ~[doris-fe.jar:1.2-SNAPSHOT]
        at org.apache.doris.nereids.trees.plans.commands.AlterSystemCommand.doRun(AlterSystemCommand.java:95) ~[doris-fe.jar:1.2-SNAPSHOT]
        at org.apache.doris.nereids.trees.plans.commands.AlterCommand.run(AlterCommand.java:40) ~[doris-fe.jar:1.2-SNAPSHOT]
        at org.apache.doris.qe.StmtExecutor.executeByNereids(StmtExecutor.java:769) ~[doris-fe.jar:1.2-SNAPSHOT]
```

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/commands/info/AddBackendOp.java

diff --git a/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/commands/info/AddBackendOp.java b/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/commands/info/AddBackendOp.java
index 8141272..43f0aed 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/commands/info/AddBackendOp.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/commands/info/AddBackendOp.java
@@ -23,6 +23,7 @@
 import org.apache.doris.qe.ConnectContext;
 import org.apache.doris.resource.Tag;
 
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -36,7 +37,7 @@
 
     public AddBackendOp(List<String> hostPorts, Map<String, String> properties) {
         super(hostPorts);
-        this.properties = properties;
+        this.properties = new HashMap<>(properties);
     }
 
     @Override

fe/fe-core/src/test/java/org/apache/doris/nereids/trees/plans/commands/AlterSystemCommandTest.java

diff --git a/fe/fe-core/src/test/java/org/apache/doris/nereids/trees/plans/commands/AlterSystemCommandTest.java b/fe/fe-core/src/test/java/org/apache/doris/nereids/trees/plans/commands/AlterSystemCommandTest.java
index e76b279..77af57e 100644
--- a/fe/fe-core/src/test/java/org/apache/doris/nereids/trees/plans/commands/AlterSystemCommandTest.java
+++ b/fe/fe-core/src/test/java/org/apache/doris/nereids/trees/plans/commands/AlterSystemCommandTest.java
@@ -87,6 +87,12 @@
         Assertions.assertThrows(AnalysisException.class, () -> addBackend2.validate(connectContext),
                 "Encounter unknown exception: errCode = 2, detailMessage = Port is out of range: 89050");
 
+        Map<String, String> properties = ImmutableMap.of("tag.compute_group_name", "another_compute_group",
+                "tag.location", "location");
+        AlterSystemCommand addBackend3 = new AlterSystemCommand(
+                new AddBackendOp(hostPorts, properties), PlanType.ALTER_SYSTEM_ADD_BACKEND);
+        Assertions.assertDoesNotThrow(() -> addBackend3.validate(connectContext));
+
         // test dropBackend
         AlterSystemCommand dropBackend = new AlterSystemCommand(
                 new DropBackendOp(hostPorts, false), PlanType.ALTER_SYSTEM_DROP_BACKEND);