krb5ccache.idl: Add definition for a Kerberos credentials cache

krb5ccache.idl: Add definition for a Kerberos credentials cache

Based on specifications found at
https://web.mit.edu/kerberos/krb5-devel/doc/formats/ccache_file_format.html

This is primarily designed for parsing and storing a single Kerberos
ticket, due to the limitations of PIDL.

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>