cmake: Add autogenerated libssh_version.h
Set the cmake project verision to the autogenerated file to have a single
point to set the version. This will be included in the libssh.h file.
Pair-Programmed-With: Andreas Schneider <email@example.com>
Signed-off-by: Heiko Thiery <firstname.lastname@example.org>
Signed-off-by: Andreas Schneider <email@example.com>
Reviewed-by: Jakub Jelen <firstname.lastname@example.org>