Support RLS for .show queries

[yunjiecao]

We have some groups that want to be assigned database admin to run some management scripts. However, we do not want these groups to be able to access senstivie data(in table and in .show queries). With RLS on tables, we could control the access to table. However, .show queries will return all data to admins which is not what we want. We want Kusto team to support RLS over .show queires so that we could better contribute to the security and compliance of data access even with admin roles.