fdo#74218 add SVG header when exporting via mtf

Change-Id: Ia200fbf73c1464160ceddc705f72d77b5f1eff51
Reviewed-on: https://gerrit.libreoffice.org/8033
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>