gh-127330: Update for OpenSSL 3.4 & document+improve the update process (GH-127331)

- Add `git describe` output to headers generated by `make_ssl_data.py`

  This info is more important than the date when the file was generated.
  It does mean that the tool now requires a Git checkout of OpenSSL,
  not for example a release tarball.

- Regenerate the older file to add the info.
  To the other older file, add a note about manual edits.

- Add notes on how to add a new OpenSSL version

- Add 3.4 error messages and multissl tests