[fix](alter) alter partition without storage_policy property will also cancel storage_policy (#51662) (#51910)

### What problem does this PR solve?

pick #51662 to branch-2.1

### Release note

None

### Check List (For Author)

- Test <!-- At least one of them must be included. -->
    - [ ] Regression test
    - [ ] Unit Test
    - [ ] Manual test (add detailed scripts or steps below)
    - [ ] No need to test or manual test. Explain why:
- [ ] This is a refactor/code format and no logic has been changed.
        - [ ] Previous test can cover this change.
        - [ ] No code files have been changed.
        - [ ] Other reason <!-- Add your reason?  -->

- Behavior changed:
    - [ ] No.
    - [ ] Yes. <!-- Explain the behavior change -->

- Does this need documentation?
    - [ ] No.
- [ ] Yes. <!-- Add document PR link here. eg:
https://github.com/apache/doris-website/pull/1214 -->

### Check List (For Reviewer who merge this PR)

- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label <!-- Add branch pick label that this PR
should merge into -->

fe/fe-core/src/main/java/org/apache/doris/alter/Alter.java

@@ -860,7 +860,9 @@ public class Alter {
                 // check currentStoragePolicy resource exist.
                 Env.getCurrentEnv().getPolicyMgr().checkStoragePolicyExist(currentStoragePolicy);
                 partitionInfo.setStoragePolicy(partition.getId(), currentStoragePolicy);
-            } else {
+            } else if (PropertyAnalyzer.hasStoragePolicy(properties)) {
+                // only set "storage_policy" = "", means cancel storage policy
+                // if current partition is already in remote storage
                 if (partition.getRemoteDataSize() > 0) {
                     throw new AnalysisException(
                         "Cannot cancel storage policy for partition which is already on code storage.");

fe/fe-core/src/main/java/org/apache/doris/common/util/PropertyAnalyzer.java

@@ -1025,6 +1025,13 @@ public class PropertyAnalyzer {
         return storagePolicy;
     }
 
+    public static boolean hasStoragePolicy(Map<String, String> properties) {
+        if (properties != null && properties.containsKey(PROPERTIES_STORAGE_POLICY)) {
+            return true;
+        }
+        return false;
+    }
+
     // analyze property like : "type" = "xxx";
     public static String analyzeType(Map<String, String> properties) throws AnalysisException {
         String type = null;