Updates to the `workspaces` object

We've made three changes to add more actions to the workspaces object, including a new field and mutation!

1. You can now query the workspaces object, rather than nesting it within a boards query.
2. You can also use the new created_at field to return the creation date of a workspace.
3. Lastly, we've added a new mutation that allows you to delete a workspace.

You can find all of the details about these updates and functionality updates in our workspaces doc!