Unable to list and return status of Instance long running operaions

#### Environment details

- OS: All
- Node.js version: v20.11.1
- npm version: 10.2.4
- `@google-cloud/spanner` version: 7.5.0

#### Steps to reproduce

* Start a long running Instance operation externally to Node.JS, for example changing size of an instance.
* Retrieve the Operation ID (`projects/xxx/instances/yyy/operations/zzz`) of this LRO
* Attempt to use the Node.JS Cloud Spanner Client Library to retrieve the status of this operation using only the Operation ID.

This is not possible - There is no public interface to list or get LROs on the instance object (by contrast there _is_ an interfacev to get the InstanceConfigOperations

* https://googleapis.dev/nodejs/spanner/latest/Instance.html
* https://googleapis.dev/nodejs/spanner/latest/v1.InstanceAdminClient.html

This is only possible using the REST API:
* https://cloud.google.com/spanner/docs/manage-and-observe-long-running-operations for how to get the status using REST API.
* https://cloud.google.com/spanner/docs/reference/rest/v1/projects.instances.operations REST operations