(fix, go): Handle deepObject query parameter arrays

[amckinney]

This fixes an issue in the Go SDK and adds support for serializing an array of struct types in the deepObject query parameter format. The format is now consistent with the TypeScript SDK (and all others).

For posterity, an example of a deepObject array is shown below:

  user, err := client.Users.Get(
    ...,
    acme.GetUserRequest{
      Filters: []*acme.Filter{
        {
          Key: "age",
          Value: "42",
        },
        {
          Key: "firstName",
          Value: "john",
        },
      },
    },
  )
  // Serialized as: ?filters[key]=age&filters[key]=firstName&filters[value]=42&filters[value]=john