If someone navigates to Multibranch pipeline that has no branches yet, SSE events do not re-render the page once said branches have runs start on them.

This exposes a bigger issue for plugins that may use branchNames(on multibranch pipeline object. Re-rendering will not happen properly as that property is not updated. Branch pipelines are still being created/deleted and SSE events come in for them, but the top level multibranchpipeline is not updated.

To fix this, when branch create/delete SSE event comes in, multibranch pipeline also needs to be refetched.