Migrations - support modifications to provisioned throughput of a table

[darrenklein]

We currently support modifications to the provisioned throughput of a global secondary index via the following migration syntax:

   alter table(:cat) do
      modify :name, :string, provisioned_throughput: [3,2]
    end

however, we do not support the ability to modify the throughput of a table. The syntax should probably be something like

    alter table(:cat, options: [
        provisioned_throughput: [2,2]
      ]) do
    end

[darrenklein]

More broadly, we need to have a way of supporting changes to a table's :options when there are no indexes being operated on - I haven't looked too deeply into this, but I'm pretty sure nothing happens due to the empty do end. This seems to be the case when attempting to update a table's billing mode, too, etc...