batches: enable filtering BC connection by multiple states

Created by: courier-new

Backend changes for https://github.com/sourcegraph/sourcegraph/issues/31164. Adds a new connection query option to provide multiple states to filter batch changes to instead of just one, like so:

{
  batchChanges(first: 20, states: [OPEN DRAFT]) {
    nodes {
      id
      ...
    }
  }
}

This new argument is available wherever batch changes are queryable, and will take precedence over a single state argument when both are supplied.

Test plan

Existing state filter tests continue to pass, additional tests for multiple states filter have been added and each combination tested.