fixed clickhouse default value handling

plugins/dbgate-plugin-clickhouse/src/backend/Analyser.js

@@ -45,6 +45,7 @@ class Analyser extends DatabaseAnalyser {
           .filter((col) => col.pureName == table.pureName)
           .map((col) => ({
             ...col,
+            defaultValue: col.defaultValue ? col.defaultValue : undefined,
             ...extractDataType(col.dataType),
           })),
         primaryKey: table.primaryKeyColumns

plugins/dbgate-plugin-clickhouse/src/frontend/Dumper.js

@@ -13,6 +13,9 @@ class Dumper extends SqlDumper {
 
     this.put('^alter ^table %f ^modify ^column %i ', newcol, newcol.columnName);
     this.columnDefinition(newcol);
+    if (oldcol.defaultValue != null && newcol.defaultValue == null) {
+      this.put(' ^remove ^default ');
+    }
     this.endCommand();
   }