s3:idmap: add a new ID mapping module autorid

s3:idmap: add a new ID mapping module autorid

This is an initial implementation of the idmap_autorid module.
It works similar to the idmap_rid module but requires less
configuration. It will automatically pick ranges for each domain,
so you do not have to bother any more about adding an idmap
configuration for all of the domains in the forest.

This is very easy to use and to configure and much more
deterministic and faster than idmap_tdb, the typical choice
of Samba users up to now.