feat: add thinking steps support as chunks to chat stream with plan and task blocks (#1824)

Co-authored-by: Michael Brooks <mbrooks@slack-corp.com>
Co-authored-by: Luke Russell <31357343+lukegalbraithrussell@users.noreply.github.com>
Co-authored-by: Maria Alejandra <104795114+srtaalej@users.noreply.github.com>