secrets.idl: add secrets_domain_info that will be used in secrets.tdb for machine...

secrets.idl: add secrets_domain_info that will be used in secrets.tdb for machine account trusts

This blob will be store in secrets.tdb. It makes it possible to store much
more useful details about the workstation trust.

The key feature that that triggered this change is the ability
to store details for the next password change before doing
the remote change. This will allow us to recover from failures.

While being there I also thought about possible new features,
which we may implement in the near future.

We also store the raw UTF16 like cleartext buffer as well as derived
keys like the NTHASH (arcfour-hmac-md5 key) and other kerberos keys.
This will allow us to avoid recalculating the keys for an in memory
keytab in future.

I also added pointer to an optional lsa_ForestTrustInformation structure,
which might be useful to implement multi-tenancy in future.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12782

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>