feat: Add metadata about the current_build / latest_build of a workspace

The idea would be to have metadata about the current_build in the coder_workspace datasource ( [https://registry.terraform.io/providers/coder/coder/latest/docs/data-sources/workspace](https://registry.terraform.io/providers/coder/coder/latest/docs/data-sources/workspace))

The available metadata that could be implemented: [https://coder.com/docs/reference/api/workspaces](https://coder.com/docs/reference/api/workspaces)

About my usecase: I would be particularly interested in the current "build\_number". I'm using an ephemeral parameter to trigger an action that should only be executed once. As I didn't integrate an ID of the build as a check, in case the dependent resources are restarted, the action is triggered an other time.

If the current "build\_number" would be accessible, this could allow an easy access to a single ID of the build, therefore that can be used for instance to trigger some actions only one time "per build".