feat: default create_index to create-only

nodejs/__test__/table.test.ts

@@ -1526,11 +1526,7 @@ describe("When creating an index", () => {
 
   it("should allow me to replace (or not) an existing index", async () => {
     await tbl.createIndex("id");
-    // Default is replace=true
-    await tbl.createIndex("id");
-    await expect(tbl.createIndex("id", { replace: false })).rejects.toThrow(
-      "already exists",
-    );
+    await expect(tbl.createIndex("id")).rejects.toThrow("already exists");
     await tbl.createIndex("id", { replace: true });
   });
 

nodejs/lancedb/indices.ts

@@ -841,7 +841,7 @@ export interface IndexOptions {
    * and the same name, then an error will be returned.  This is true even if
    * that index is out of date.
    *
-   * The default is true
+   * The default is false
    */
   replace?: boolean;