Document fleet selector in the databricks_node_type data source (#2261)

Document it after it became publicly available

Author: alexott

docs/data-sources/node_type.md

@@ -57,6 +57,7 @@ Data source allows you to pick groups by the following attributes
 * `photon_worker_capable` - (Optional) Pick only nodes that can run Photon workers. Defaults to *false*.
 * `photon_driver_capable` - (Optional) Pick only nodes that can run Photon driver. Defaults to *false*.
 * `graviton` - (boolean, optional)  if we should limit the search only to nodes with AWS Graviton CPUs. Default to *false*.
+* `fleet` - (boolean, optional)  if we should limit the search only to [AWS fleet instance types](https://docs.databricks.com/compute/aws-fleet-instances.html). Default to *false*.
 * `is_io_cache_enabled` - (Optional) . Pick only nodes that have IO Cache. Defaults to *false*.
 * `support_port_forwarding` - (Optional) Pick only nodes that support port forwarding. Defaults to *false*.