[JENKINS-75726] Set proper content type and encoding (#406)

Author: mawinter69

src/main/java/com/michelin/cio/hudson/plugins/rolestrategy/RoleBasedAuthorizationStrategy.java

@@ -1008,6 +1008,7 @@ public void doGetRoleAssignments(@QueryParameter(fixEmpty = true) String type) t
       userEntry.put("roles", roles);
       responseJson.add(userEntry);
     }
+    Stapler.getCurrentResponse2().setContentType("application/json;charset=UTF-8");
     Writer writer = Stapler.getCurrentResponse2().getWriter();
     responseJson.write(writer);
     writer.close();