[apache#6384] fix: Gravitino default JVM config mismatches with comments from gravitino-env.sh (apache#6385)

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### What changes were proposed in this pull request?

Update Gravitino JVM memory default.

### Why are the changes needed?

Fix: apache#6384

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

No test

Author: puchengy

bin/common.sh.template

@@ -106,7 +106,7 @@ function addDirToClasspath(){
 }
 
 if [[ -z "${GRAVITINO_MEM}" ]]; then
-  export GRAVITINO_MEM="-Xmx1024m"
+  export GRAVITINO_MEM="-Xms1024m -Xmx1024m -XX:MaxMetaspaceSize=512m"
 fi
 
 if [[ -n "${JAVA_HOME}" ]]; then