rebase with upstream release 0.38 (rhbz#2234464)
    
    - Support relative lastmod queries.
    - Support indexing of designated attachments as text.
    - Emacs: Introduce notmuch-tree-outline-mode.
    - Emacs: Some compatibility fixes for Emacs 29. At least one issue (hiding
      images) remains in 0.38.
    - Various bugfixes and performance improvements.