[Fix](InternalSchema) Compute nodes should not be used for Internal s…

…chema three replica (apache#36130)

## Proposed changes

Issue Number: close #xxx

When I add computing nodes to the cluster, a large number of warning
logs will appear in the FE log, as shown below:

```
2024-06-11 17:50:04,360 WARN (InternalSchemaInitializer|137) [InternalSchemaInitializer.modifyTblReplicaCount():146] Failed to scale replica of stats tbl:column_statistics to 3
org.apache.doris.common.AnalysisException: errCode = 2, detailMessage = errCode = 2, detailMessage = Failed to find enough backend, please check the replication num,replication tag and storage medium and avail capacity of backends.
Create failed replications:
replication tag: {"location" : "default"}, replication num: 3, storage medium: null
    at org.apache.doris.common.util.PropertyAnalyzer.analyzeReplicaAllocationImpl(PropertyAnalyzer.java:1217) ~[doris-fe.jar:1.2-SNAPSHOT]
    at org.apache.doris.common.util.PropertyAnalyzer.analyzeReplicaAllocation(PropertyAnalyzer.java:1136) ~[doris-fe.jar:1.2-SNAPSHOT]
    at org.apache.doris.catalog.Env.modifyTableReplicaAllocation(Env.java:4868) ~[doris-fe.jar:1.2-SNAPSHOT]
    at org.apache.doris.catalog.InternalSchemaInitializer.modifyTblReplicaCount(InternalSchemaInitializer.java:123) ~[doris-fe.jar:1.2-SNAPSHOT]
    at org.apache.doris.catalog.InternalSchemaInitializer.run(InternalSchemaInitializer.java:93) ~[doris-fe.jar:1.2-SNAPSHOT]
```


![image](https://github.com/apache/doris/assets/24907215/53ea2f34-1012-4f96-a2c9-be9c2b39b772)

This is because the computing node is also considered a replica in the
code, and the computing node does not have storage resources, resulting
in an error message.

---------

Co-authored-by: camby <[email protected]>

fe/fe-core/src/main/java/org/apache/doris/catalog/InternalSchemaInitializer.java

@@ -109,7 +109,7 @@ public static void modifyTblReplicaCount(Database database, String tblName) {
             return;
         }
         while (true) {
-            int backendNum = Env.getCurrentSystemInfo().getBackendNumFromDiffHosts(true);
+            int backendNum = Env.getCurrentSystemInfo().getStorageBackendNumFromDiffHosts(true);
             if (FeConstants.runningUnitTest) {
                 backendNum = Env.getCurrentSystemInfo().getAllBackendIds().size();
             }

fe/fe-core/src/main/java/org/apache/doris/system/SystemInfoService.java

@@ -420,11 +420,11 @@ public List<Backend> getCnBackends() {
     }
 
     // return num of backends that from different hosts
-    public int getBackendNumFromDiffHosts(boolean aliveOnly) {
+    public int getStorageBackendNumFromDiffHosts(boolean aliveOnly) {
         Set<String> hosts = Sets.newHashSet();
         ImmutableMap<Long, Backend> idToBackend = idToBackendRef;
         for (Backend backend : idToBackend.values()) {
-            if (aliveOnly && !backend.isAlive()) {
+            if ((aliveOnly && !backend.isAlive()) || backend.isComputeNode()) {
                 continue;
             }
             hosts.add(backend.getHost());