feat: allow setting train=False and name on indices (#2586)

Enables two new parameters when building indices:

* `name`: Allows explicitly setting a name on the index. Default is
`{col_name}_idx`.
* `train` (default `True`): When set to `False`, an empty index will be
immediately created.

The upgrade of Lance means there are also additional behaviors from
https://github.com/lancedb/lance/commit/cd76a993b8b65877135cb9cfb47448a761ac7f7b:

* When a scalar index is created on a Table, it will be kept around even
if all rows are deleted or updated.
* Scalar indices can be created on empty tables. They will default to
`train=False` if the table is empty.

---------

Co-authored-by: Weston Pace <weston.pace@gmail.com>

docs/src/js/interfaces/IndexOptions.md

@@ -26,6 +26,18 @@ will be used to determine the most useful kind of index to create.
 
 ***
 
+### name?
+
+```ts
+optional name: string;
+```
+
+Optional custom name for the index.
+
+If not provided, a default name will be generated based on the column name.
+
+***
+
 ### replace?
 
 ```ts
@@ -42,8 +54,27 @@ The default is true
 
 ***
 
+### train?
+
+```ts
+optional train: boolean;
+```
+
+Whether to train the index with existing data.
+
+If true (default), the index will be trained with existing data in the table.
+If false, the index will be created empty and populated as new data is added.
+
+Note: This option is only supported for scalar indices. Vector indices always train.
+
+***
+
 ### waitTimeoutSeconds?
 
 ```ts
 optional waitTimeoutSeconds: number;
 ```
+
+Timeout in seconds to wait for index creation to complete.
+
+If not specified, the method will return immediately after starting the index creation.