Build table with access permissions for RAPI resources

Sometimes it can be difficult to determine the access permissions needed
for a certain RAPI resource without looking at code. This table, added
at the end of “rapi.rst”, shows all resources and the permissions needed
for their methods.

Another nice side-effect of this change is that there's an automatic
cross-checking between implemented resources and methods and the
documentation.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>