add AgentAssignmentDao

src/main/java/cz/fi/muni/pa165/seminar4/group7/secretservice/dao/AgentAssignmentDao.java

+package cz.fi.muni.pa165.seminar4.group7.secretservice.dao;
+
+import cz.fi.muni.pa165.seminar4.group7.secretservice.entity.AgentAssignment;
+import org.springframework.data.repository.CrudRepository;
+
+public interface AgentAssignmentDao extends CrudRepository<AgentAssignment, Long> {
+}