Get a single grant given to an entity. This calls returns any permission
to take the specified action against the specified resource on the
requested entity.

Access Control:

• The calling principal must have either "listGrants" or "share" action permission for the resource "{resourceHrn}" in the "authorization" service.
• The realm of the calling principal MUST match the realm of the requested app.
• The calling principal MUST NOT include a project scope.